CA1269150A - Apparatus and method for monitoring low-level combustibles - Google Patents
Apparatus and method for monitoring low-level combustiblesInfo
- Publication number
- CA1269150A CA1269150A CA000530556A CA530556A CA1269150A CA 1269150 A CA1269150 A CA 1269150A CA 000530556 A CA000530556 A CA 000530556A CA 530556 A CA530556 A CA 530556A CA 1269150 A CA1269150 A CA 1269150A
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- CA
- Canada
- Prior art keywords
- level
- pulverizing mill
- coal pulverizing
- signal
- mill
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
- B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
- B02C23/00—Auxiliary methods or auxiliary devices or accessories specially adapted for crushing or disintegrating not provided for in preceding groups or not specially adapted to apparatus covered by a single preceding group
- B02C23/18—Adding fluid, other than for crushing or disintegrating by fluid energy
- B02C23/24—Passing gas through crushing or disintegrating zone
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
- B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
- B02C23/00—Auxiliary methods or auxiliary devices or accessories specially adapted for crushing or disintegrating not provided for in preceding groups or not specially adapted to apparatus covered by a single preceding group
- B02C23/04—Safety devices
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- Engineering & Computer Science (AREA)
- Food Science & Technology (AREA)
- Disintegrating Or Milling (AREA)
- Crushing And Grinding (AREA)
Abstract
APPARATUS AND METHOD FOR
MONITORING LOW-LEVEL COMBUSTIBLES
ABSTRACT OF THE DISCLOSURE
A safety control system for a coal pulverizing mill is disclosed. The control system utilizes measurements of the net oxygen level and the carbon monoxide equivalent (COe) level of the combustible gases within the pulverizing mill.
First levels of the net oxygen and the rate of carbon mono-xide equivalent change in the pulverizing mill are utilized in a control logic system to actuate alarms. Second levels of the net oxygen and the carbon monoxide equivalent (COe) level in the pulverizing mill are utilized to accomplish the inerting of the mill.
MONITORING LOW-LEVEL COMBUSTIBLES
ABSTRACT OF THE DISCLOSURE
A safety control system for a coal pulverizing mill is disclosed. The control system utilizes measurements of the net oxygen level and the carbon monoxide equivalent (COe) level of the combustible gases within the pulverizing mill.
First levels of the net oxygen and the rate of carbon mono-xide equivalent change in the pulverizing mill are utilized in a control logic system to actuate alarms. Second levels of the net oxygen and the carbon monoxide equivalent (COe) level in the pulverizing mill are utilized to accomplish the inerting of the mill.
Description
i91ri~[) Case /~767 ~P~ATU~ ~ND METI~OD FOR
MON~TORING LOW-LEVEL COM~USTIBL~S
TECHNICAL FIELD
The present invention generally relates to control systems for pulverizers and more particularly to an im-proved safety control system for detecting and controllin impending hazardous conditions in a coal pulverizing mill BACKGRO~ND ~RT
Coal usaqe has increasedin the ~nited States for a variety of reasons, particularly those of an economic nature.
The utility industry is burning far more coal today than it did ten years aqo. ~ith the increased demand for coal, the use of younger, more volatile coals like subbituminous and lignite has increased. Consequently, the potential for spon-taneous combustioll causing serious fires and explosions duringthe handling, qrinding and pulverizing steps has increased.
Several methods which have been given considerable atten-tion for detecting impending pulverizing mill fires are base~
on measurinq temperature, gas flow velocity and carbon monoxide.
Single and multiple point temperature monitoring tecllniques have been used for a number of years to warn of an over-tem-perature condition in the mill. This approach, however, provides information too late to stop a fire from spreading.
The qas flow velocity monitor approach has potential, but the relationship hetween gas flow, temperature and pressure are 9~S() not sufficiently understood to he effective as a warninq system~ T~e increase in the carhon monoxide level in the pulverizlng mill has been recently given the most atten-tion in research and practice and is a way o detectingpulverizing mill fires.
~ numher o commercial devices utilizing infrared ahsorption techniques are available for monitoring carl-on monoxide levels in the pulverizing mi]l. ~his method is based upon the principle that when coal starts to oxidize, i.e. the early stages of combustion, carbon monoxide is produced. 8eing ahle to detect this carhon monoxide at very low levels e.q. 25 to 50 ppm permits the mill operator to take precautionary measures to prevent a major fire or an explosion in the mill.
~ small pocket of oxidizing coal can become a ma~or fire through escalation or ignition. If escalation occurs the oxidation process intensifies as the quantity of coal involved and temperature increase. Larqer quantities of carhon monoxi~e are produced as the process escalates until a runaway con~
tion is reached which results in a fire. This small quantity of oxidizinq coal also represents an iqnition source wllicl) combined with the other elements within the mill can resu]t in a ma~or fire or explosion. In this case, the quantity of carbon monoxide does not need to escalate prior to the fire or explosion since the small pocket of oxidizing coal is only an ignition source. From the foreqoing it is apparellt that detection ~ethods based upon carbon monoxide alone are use-ful only after oxidation has started and do not give tlle operator a good indication of potentially explosive conditions within the pulverizing mill. Other factors such as the level of oxygen and combustible gases in the pulverizing mill, must he considered when evaluating the possibility of a fire or an explosion within the pulverizing mill.
1~9150 Because oE the Eoregoing it has become desirable to develop an improved safety control system for a pulverizing mill wherein a measurement of oxygen an and aggregate measurement of not only carbon monoxide but all combustible gases in the mill are made and utilized Eor controlling the operation of the mill and warning the operator of a potentially dangerous mill condition.
The invention provides an improved safety system for a coal pulverizing mill comprising means for determining the rate of change of the level of carbon monoxide and other combustible gases in the coal pulverizing mill and establishing a signal indicative thereoE; means for comparing said signal from said determlning means with a predetermined setpoint signal indicative of a potentially hazardous rate of change of the level of carbon monoxide and other combustible gases in the coal pulverizing mill and establishing a first control signal therefrom; and alarm means responsive to said first control signal for indicating a potentially hazardous condition in the coal pulverizing mill.
The invention also provides an improved safety system for a coal pulverizing mill comprising means for measuring the level of carbon monoxide and other gases in the coal pulverizing mill and establishing a signal indicative thereof; means for comparing said signal from said measuring means with a predetermined setpoint signal indicative of a hazardous level of carbon monoxide and other combustible gases in the coal pulverizing mill and establishing a first control signal therefrom; and inerting means responsive to said first control signal for inerting the coal pulverizing mill. In the preferred form, a single point analyzer is used which is mounted directly to the pulverizing mill to provide continuous measurements of both the oxygen content and the carbon monoxide equivalent (COe) level of the pulverizing mill atmosphere. The measurement of the carbon monoxide equivalent (COe) level includes not only the level of carbon monoxide in the pulverizing mill but also the other combustible gases, such as hydrogen, methane, ethane, etc., in the mill. The oxygen portion of the analyzer uses a sensor operating at a temperature where any combustible volatile material will combine with the oxygen in the sample that is extracted from the pulverizing mill. The sensor will then respond to the free or uncombined oxygen remaining. The resulting measurement, referred to as the net oxygen (2) level, is then compared with various predetermined setpoints and correlated with the carbon monoxide (CO ) level, which is similarly compared with various predetermined setpoints, to determine if a potentially dangerous condition exists within the pulverizing mill. Thus, measurements of both the net oxygen (2) level and the carbon monoxide equivalent (CO ) level in the pulverizing mill atmosphere are used to determine the onset of conditions witlli1l the mill w11ieh might lea~ to a fire or explosion in same.
Bl~lEE DESCRlP'rION OF 5`11E DRA~INGS
Figure l is a schematic drawinq of the safety control systern of the present invention.
Figure 2 is a schematic drawinq of the monitorinq a11c1 control logic assernhly of the safety control system illus-trated in Figure l.
Figure 3 is a graph of the relationship of the carbon monoxide equivalent (COe) level and the net oxygen (2) level in a coal pulverizing mill to the various combustible components which comprise same versus coal temperature.
Figure 4 is a graph of the relationship of the carboTl monoxide equivalent (COe) level and the net oxygen (2) level in a pulverizing mill versus time and illustrates the ch~nqcs in these levels when a fire occurs in the mill.
Figure 5 is a graph of the relationship of the carbon monoxide equivalent (COe) level and the net oxygen (2) level
MON~TORING LOW-LEVEL COM~USTIBL~S
TECHNICAL FIELD
The present invention generally relates to control systems for pulverizers and more particularly to an im-proved safety control system for detecting and controllin impending hazardous conditions in a coal pulverizing mill BACKGRO~ND ~RT
Coal usaqe has increasedin the ~nited States for a variety of reasons, particularly those of an economic nature.
The utility industry is burning far more coal today than it did ten years aqo. ~ith the increased demand for coal, the use of younger, more volatile coals like subbituminous and lignite has increased. Consequently, the potential for spon-taneous combustioll causing serious fires and explosions duringthe handling, qrinding and pulverizing steps has increased.
Several methods which have been given considerable atten-tion for detecting impending pulverizing mill fires are base~
on measurinq temperature, gas flow velocity and carbon monoxide.
Single and multiple point temperature monitoring tecllniques have been used for a number of years to warn of an over-tem-perature condition in the mill. This approach, however, provides information too late to stop a fire from spreading.
The qas flow velocity monitor approach has potential, but the relationship hetween gas flow, temperature and pressure are 9~S() not sufficiently understood to he effective as a warninq system~ T~e increase in the carhon monoxide level in the pulverizlng mill has been recently given the most atten-tion in research and practice and is a way o detectingpulverizing mill fires.
~ numher o commercial devices utilizing infrared ahsorption techniques are available for monitoring carl-on monoxide levels in the pulverizing mi]l. ~his method is based upon the principle that when coal starts to oxidize, i.e. the early stages of combustion, carbon monoxide is produced. 8eing ahle to detect this carhon monoxide at very low levels e.q. 25 to 50 ppm permits the mill operator to take precautionary measures to prevent a major fire or an explosion in the mill.
~ small pocket of oxidizing coal can become a ma~or fire through escalation or ignition. If escalation occurs the oxidation process intensifies as the quantity of coal involved and temperature increase. Larqer quantities of carhon monoxi~e are produced as the process escalates until a runaway con~
tion is reached which results in a fire. This small quantity of oxidizinq coal also represents an iqnition source wllicl) combined with the other elements within the mill can resu]t in a ma~or fire or explosion. In this case, the quantity of carbon monoxide does not need to escalate prior to the fire or explosion since the small pocket of oxidizing coal is only an ignition source. From the foreqoing it is apparellt that detection ~ethods based upon carbon monoxide alone are use-ful only after oxidation has started and do not give tlle operator a good indication of potentially explosive conditions within the pulverizing mill. Other factors such as the level of oxygen and combustible gases in the pulverizing mill, must he considered when evaluating the possibility of a fire or an explosion within the pulverizing mill.
1~9150 Because oE the Eoregoing it has become desirable to develop an improved safety control system for a pulverizing mill wherein a measurement of oxygen an and aggregate measurement of not only carbon monoxide but all combustible gases in the mill are made and utilized Eor controlling the operation of the mill and warning the operator of a potentially dangerous mill condition.
The invention provides an improved safety system for a coal pulverizing mill comprising means for determining the rate of change of the level of carbon monoxide and other combustible gases in the coal pulverizing mill and establishing a signal indicative thereoE; means for comparing said signal from said determlning means with a predetermined setpoint signal indicative of a potentially hazardous rate of change of the level of carbon monoxide and other combustible gases in the coal pulverizing mill and establishing a first control signal therefrom; and alarm means responsive to said first control signal for indicating a potentially hazardous condition in the coal pulverizing mill.
The invention also provides an improved safety system for a coal pulverizing mill comprising means for measuring the level of carbon monoxide and other gases in the coal pulverizing mill and establishing a signal indicative thereof; means for comparing said signal from said measuring means with a predetermined setpoint signal indicative of a hazardous level of carbon monoxide and other combustible gases in the coal pulverizing mill and establishing a first control signal therefrom; and inerting means responsive to said first control signal for inerting the coal pulverizing mill. In the preferred form, a single point analyzer is used which is mounted directly to the pulverizing mill to provide continuous measurements of both the oxygen content and the carbon monoxide equivalent (COe) level of the pulverizing mill atmosphere. The measurement of the carbon monoxide equivalent (COe) level includes not only the level of carbon monoxide in the pulverizing mill but also the other combustible gases, such as hydrogen, methane, ethane, etc., in the mill. The oxygen portion of the analyzer uses a sensor operating at a temperature where any combustible volatile material will combine with the oxygen in the sample that is extracted from the pulverizing mill. The sensor will then respond to the free or uncombined oxygen remaining. The resulting measurement, referred to as the net oxygen (2) level, is then compared with various predetermined setpoints and correlated with the carbon monoxide (CO ) level, which is similarly compared with various predetermined setpoints, to determine if a potentially dangerous condition exists within the pulverizing mill. Thus, measurements of both the net oxygen (2) level and the carbon monoxide equivalent (CO ) level in the pulverizing mill atmosphere are used to determine the onset of conditions witlli1l the mill w11ieh might lea~ to a fire or explosion in same.
Bl~lEE DESCRlP'rION OF 5`11E DRA~INGS
Figure l is a schematic drawinq of the safety control systern of the present invention.
Figure 2 is a schematic drawinq of the monitorinq a11c1 control logic assernhly of the safety control system illus-trated in Figure l.
Figure 3 is a graph of the relationship of the carbon monoxide equivalent (COe) level and the net oxygen (2) level in a coal pulverizing mill to the various combustible components which comprise same versus coal temperature.
Figure 4 is a graph of the relationship of the carboTl monoxide equivalent (COe) level and the net oxygen (2) level in a pulverizing mill versus time and illustrates the ch~nqcs in these levels when a fire occurs in the mill.
Figure 5 is a graph of the relationship of the carbon monoxide equivalent (COe) level and the net oxygen (2) level
2~ in a coal pulverizing mill versus time and illustrates the changes in these levels when a smoldering fire exists in the mill but ignition doe~s not occur.
Figure 6 is a qraph of the net oxygen (2~ level versus carhon monoxide equivalent (COe) level in a pulverizinq mill and illustrates the manner in which mill operating con-ditiorls depend upon the foregoing levels.
DE~CRIPTION OF TIIE PREFERRED EMBODI~ENT
Referring now to the drawings where the illustrations are for the purpose of describing the preferred emhodiment of the present invention and are not intended to limit the inven-tion hereto, Figure l is a schematic drawing of the safety control system ln of the present invention. As such, the l~ 15~
control s~stem 10 can be integrated in a facility s control systern desi~ned to monitor the performance of and detect impending fire or explosions in industrial coal pulveri7illq mills ~y monitoring the net oxygen (2) level and tile call~on monoxide equivalent (COe~ level of the combustible colm~ollents in the pulverizing mil] atmospllere. The measurement of the carbon monoxide equivalent (COe) level of the combustible com-ponents includes not only carbon monoxide but also other combustibles components such as hydrogen methane ethane and other iligher hvdrocarbon components. The combined measure-ment of the Ce and net 2 levels in the pulverizing mill atmosphere is used to indicate the oxidation rate of the coal to prevent spontaneous combustion within the mill. Jn addition the measurement of the net 2 level, when comhine(l with other measurements can provide the basis for overall mill performance calculations and the quality of the pul-verized c~al.
As shown in Figure 1, the COe/o2 sample probe 12 is usually placed in a coal pulverizing mill 14 outlet zone.
A sample qas is drawn throuqh the probe 12 which is provid~N
with a high temperature filter 16. The filter 16 is requ;re-l to maintain trouble-free operation of the control system 1~
by minimizing the amount of particulate matter drawn into the analyzer. A filter 16 which can be used for this application is of a type described in U.S. Patent No. 4,286,472.
Tlle air sample drawn from the coal pulverizer is the anal~zed for percent by volume of oxvqen (2) content an~i the carbon monoxide equivalent (COe) concentration of combus-tible components in ppm (parts per million) via a known o~yqenand Ce gas analyzer 18 designed to operate in a harsh power plant environment and havinq autocalibration capabilities.
Elect.rical signals corresponding to the net oxygen (2) level i.e., the level of the free or uncomhined oxyqen withill the sample remaininq after the combustible volatile mater-ials therein have combined with the oxyqen in tile sampl~, and the c~rhon monoxide equivalent (COe) level are trans-rnitted respecti~ely to a monitoring and control logic a.ssenl-bly 20 located in a central control room via lines 22 and 24.
The net O~ and Ce levels are displayed and/or recorded on a strip-chart: recorder 26. If the net 2 level falls helow a predetermined rise level, the system 10 actuates audible and visihle alarms 28, 30, respectively, to alertthe operator who, in turn, may manually take corrective action to inert the pulverizinq mill 14 or permit the system 10 to continue until it initiates an automatic inert mode of operation to bring the pulverizing mill 14 operating parameters back under control.
Referring now to Figure 2, the monitoring and contro]
logic assemhly 20 utilizes both the net oxygen (2) measure-ment provided by the analyzer i8 along line 22 as well as the carbon monoxide equivalent (COe) measurement provided along line 24 from the analyzer 18 to actuate the alarms 28, 30, respectively at a predetermined net oxygen (2) level and at a predetermined carhon monoxide equivalent (COe) rise level. In addition, when the net oxygen (2) level and/or the absolute carbon monoxide equivalent (COe) level exceed certain critical limits, automatic inerting of the pulveriz-ing mill 14 is undertaken by controlling the opening of a valve 32 whic)l permits some inerting media, such as carbon dioxide or steam, to flow along a line 34 into the pulverizinq mill 14.
~ s for the alarm functions, the net oxygen (2~ measure-ment from line 22 is transmitted along a line 36 to a differ-ence station 38 having a setpoint set at a predetermined net oxygen control point provided along a line 4G. The difference 915(t - station 38 conpares the actual net oxyqen (2) measurerlent provile~ by the analyzer 1~ with the setpoint net oxy~l-n Ievel and provides an error siqnal alonq a line 42 whith is one input to an ~ND gate 44 rhe other input to tle ~NI) qate 44 is provi(le~l by a constant neqative signal fron a ~re(leter-mined source along a line 46 Thus as long as tle net oxyqe (2) level proviled to the difference station 38 is qre.t-r than setpoint net oxyqen level a positive error signal wi~l be transmitted along line 42 to the ~ND gate 44 which will then fail to provide any control signal alone a line 48 thus failing to actuate the alarm 28 As soon as the net oxy~en (2) level lrops helow the setpoint net oxygen level the error signal transmitted along line 42 will become negative an~ in combination with the constant negative signal proviletl on line 46 resilts in the conduction of the AND gate 44 causinq a con-trol siqnal to he transmitted along line 4~ to the alarm 28 actuating SAme and providing an indication of potential rro-blems with respect to the atmosphere in the pulverizinq Ini.ll Alternatively the signal representAtive of the meisllre(l carbon monoxide equivalent (COe) level which is transmit~d along line 24 may also provide an actuation of the alternate alarm 30 The measure-3 carbon monoxide equivalent (CO2) leve]
signal is transmitted to a derivative action controller 5() which is sensitive to any variations in the carbon monoxide equivalent (COe) level and provides an output signal alon~ a line 52 indicative of the slope or rate of change of the car-bon monoxide equivalent (COe) level in the pulverizing mill 1 The output of the derivative action controller 50 is trans-mitted along line 52 to a difference station 54 having a pre-determined setpoint providel along 2 line 56 r-presentative of a rate of change of the carbon monoxide equivalent (COe) level which wouli indicate coal ignition in the pulverizinq mill l~i 1;~691~
The output of the difference station 54 is transmitted alonq a line 58 to an ~ gate 60 having a second input ofa cOn-stant positive value provided alonq a line 62. In oc?eration, the rate of chanqe of the carbon monoxide equivalent (COr) level normAl.Ly stays below the setpoint applied to the ~lir-ference s~ation 54 resultinq in a negative output siqnal from this station 54 alonq line 58. ~henever the actual r~te of change of the carbon monoxicle equivalent (COe) level in the pulverizinq mill exceeds the setpoint provided alonq line 56 to this difference station 54, the signal transmitted along line 58 becomes positive, causing the AND gate 60 to concluct resulting in the transmission of a control siqnal alonq a line 64 to the alarm 8n actuating same to indicate the existence of a potentially dangerous condition in the pulveri%ing mill 14.
The foregoing alarms 28 and 30, when actuated, warn the operator of a potentially dangerous condition in the pulveriz-ing mill 14. These alarms should indicate to the operator that close monitoring of the pulverizing mill 14 is required and generally one al~rm will be actuated, possihly followecl by a second alarm. Since the inerting of the pulverizinq mill 14 may shock the pulverizer, such inerting is left to the discretion of the operator. There are, however, certnin conditions beyond which inerting of the pulverizinq mill 14 is mandatory and must be automatically initiated. To provide for such automatic inerting of the pulverizing mi.ll 14, the control system 10 again utilizes both the net oxygen (2~ measurements and the carbon monoxide equivalent (COe) measurements provided via lines 22 and 24, respectively.
~ utomatic inerting of the pulverizinq mill 14 is actuated by a difference station 66 which has a net oxygen level set-point provided to it along a line 68. The net oxygen level 5~
_9_ setpoint provided to the difference station 66 is signifi-cantly lower thall the setpoint level provided to the differ--ence station 38 Tllus ~luring normal operation of the p~
verizinq mill l4 the net o yqen (2~ level measured and transmittel to the difference station 66 will exceed thc setpoint applie(l thereto and the error signal pro~uced hy tlle differel~(e statioll 66 will be a positive signal which is transmitte~l aloncl a line 70 to an ~ND gate 72. The other in-put of tne ~N~ gate 72 is provided by a constant negativesignal along a line 74. Thus during normal operation of the pulverizinq mill 14 the inouts to the ~ qate 72 will he positive and negative resulting in no control signal be;nq transmitted froln the ~ND gate 72 alonq a line 76. Whenever the net oxyqen (2) level within the pulverizing mill 14 falls below the setpoint level applied to the ~ifference station 66 the output of this station 66 becomes negative providinq two negative inpu.s to the ~ND gate 72 resulting in the transllis-sion of a control signal along line 76 to a switching cir-cuit 78 The switclling circuit 78 is a normally open cir-cuit preventing the signal from a controller 80 from reach-ing the control valve 32. When a control siqnal is present along line 76 the switching circuit 78 changes to a closed circuit condition which results in the controller 80 beinq responsib]e for tle operation of the valve 32.
One inpl]t to the controller 80 is the actual net oxyg~n ~2) level in the pulverizing mill 14 and is provided by a line 82 which is connected to line 22. The setpoint for the con-troller 8n is provided along a line 84 from some setpoint sta-tion and tlle level of this setpoint is typically between t)esetpoint levels for difference stations 66 and 38. Thus when the switching circuit 78 is actuate~ by a control signal from the ~ND gate 72 in~iicating that the net oxygen (2) level within the pulverizing mill 14 has fallen below the set-point level to the ~ifference station 66 the controller 8n ~69~ jO
will open valve 32 causinq an inertinq atmosphere, such as carbon dioxide, to be delivered to the pulverizing mill 14 until a somewhat normal net oxYqen level is reached close to the setpoir-t ~evel for the controller 8n. Typica]ly, 1 he setpoint level for the controller 8n is kept some~hat lo-rer than normal atmosphere to minimize the shock to the pul~;er-izer 14 due to the inertinq process. When the net oxyqen (2) level in the pulverizing mill lq reaches the setpoint level for the controller 80, the .switching circuit 78 can then be reset to its normally open condition by a reset sigr)al along a line 86 from either a manual source or an automatic source tied to some parameter indicative of the establishment of normal operating conditions within the pulverizing mill 14.
The actuation of the automatic inertinq means is also alternatively done upon the sensing of a predetermined ahso-lute carbon monoxide equivalent (COe) level in the pulveriz-ing mill 14. The carbon monoxide equivalent (CO~) siqna~
normally provided on line 24 is tapped hy a line 88 to pro-vide one input to a difference station 90. The setpoint of the difference station 90 is provided alonq a line 92 from a setpoint station and the level of this setpoint ic typically set at the maximum carbon monoxide equivalent (COe) level which can he tolerated in the pulverizinq mill 14. Thus, as long as the carbon monoxide equivalent (COe) level stays below the setpoint for the difference station 90, a positive error signal will be transmitte~ by the dif-ference station sn along a line 9q to an ~ND gate 96. The other input to the ~ND gate 9fi is a constant negative siq-nal provided along a line 98. Thus, during normal operation
Figure 6 is a qraph of the net oxygen (2~ level versus carhon monoxide equivalent (COe) level in a pulverizinq mill and illustrates the manner in which mill operating con-ditiorls depend upon the foregoing levels.
DE~CRIPTION OF TIIE PREFERRED EMBODI~ENT
Referring now to the drawings where the illustrations are for the purpose of describing the preferred emhodiment of the present invention and are not intended to limit the inven-tion hereto, Figure l is a schematic drawing of the safety control system ln of the present invention. As such, the l~ 15~
control s~stem 10 can be integrated in a facility s control systern desi~ned to monitor the performance of and detect impending fire or explosions in industrial coal pulveri7illq mills ~y monitoring the net oxygen (2) level and tile call~on monoxide equivalent (COe~ level of the combustible colm~ollents in the pulverizing mil] atmospllere. The measurement of the carbon monoxide equivalent (COe) level of the combustible com-ponents includes not only carbon monoxide but also other combustibles components such as hydrogen methane ethane and other iligher hvdrocarbon components. The combined measure-ment of the Ce and net 2 levels in the pulverizing mill atmosphere is used to indicate the oxidation rate of the coal to prevent spontaneous combustion within the mill. Jn addition the measurement of the net 2 level, when comhine(l with other measurements can provide the basis for overall mill performance calculations and the quality of the pul-verized c~al.
As shown in Figure 1, the COe/o2 sample probe 12 is usually placed in a coal pulverizing mill 14 outlet zone.
A sample qas is drawn throuqh the probe 12 which is provid~N
with a high temperature filter 16. The filter 16 is requ;re-l to maintain trouble-free operation of the control system 1~
by minimizing the amount of particulate matter drawn into the analyzer. A filter 16 which can be used for this application is of a type described in U.S. Patent No. 4,286,472.
Tlle air sample drawn from the coal pulverizer is the anal~zed for percent by volume of oxvqen (2) content an~i the carbon monoxide equivalent (COe) concentration of combus-tible components in ppm (parts per million) via a known o~yqenand Ce gas analyzer 18 designed to operate in a harsh power plant environment and havinq autocalibration capabilities.
Elect.rical signals corresponding to the net oxygen (2) level i.e., the level of the free or uncomhined oxyqen withill the sample remaininq after the combustible volatile mater-ials therein have combined with the oxyqen in tile sampl~, and the c~rhon monoxide equivalent (COe) level are trans-rnitted respecti~ely to a monitoring and control logic a.ssenl-bly 20 located in a central control room via lines 22 and 24.
The net O~ and Ce levels are displayed and/or recorded on a strip-chart: recorder 26. If the net 2 level falls helow a predetermined rise level, the system 10 actuates audible and visihle alarms 28, 30, respectively, to alertthe operator who, in turn, may manually take corrective action to inert the pulverizinq mill 14 or permit the system 10 to continue until it initiates an automatic inert mode of operation to bring the pulverizing mill 14 operating parameters back under control.
Referring now to Figure 2, the monitoring and contro]
logic assemhly 20 utilizes both the net oxygen (2) measure-ment provided by the analyzer i8 along line 22 as well as the carbon monoxide equivalent (COe) measurement provided along line 24 from the analyzer 18 to actuate the alarms 28, 30, respectively at a predetermined net oxygen (2) level and at a predetermined carhon monoxide equivalent (COe) rise level. In addition, when the net oxygen (2) level and/or the absolute carbon monoxide equivalent (COe) level exceed certain critical limits, automatic inerting of the pulveriz-ing mill 14 is undertaken by controlling the opening of a valve 32 whic)l permits some inerting media, such as carbon dioxide or steam, to flow along a line 34 into the pulverizinq mill 14.
~ s for the alarm functions, the net oxygen (2~ measure-ment from line 22 is transmitted along a line 36 to a differ-ence station 38 having a setpoint set at a predetermined net oxygen control point provided along a line 4G. The difference 915(t - station 38 conpares the actual net oxyqen (2) measurerlent provile~ by the analyzer 1~ with the setpoint net oxy~l-n Ievel and provides an error siqnal alonq a line 42 whith is one input to an ~ND gate 44 rhe other input to tle ~NI) qate 44 is provi(le~l by a constant neqative signal fron a ~re(leter-mined source along a line 46 Thus as long as tle net oxyqe (2) level proviled to the difference station 38 is qre.t-r than setpoint net oxyqen level a positive error signal wi~l be transmitted along line 42 to the ~ND gate 44 which will then fail to provide any control signal alone a line 48 thus failing to actuate the alarm 28 As soon as the net oxy~en (2) level lrops helow the setpoint net oxygen level the error signal transmitted along line 42 will become negative an~ in combination with the constant negative signal proviletl on line 46 resilts in the conduction of the AND gate 44 causinq a con-trol siqnal to he transmitted along line 4~ to the alarm 28 actuating SAme and providing an indication of potential rro-blems with respect to the atmosphere in the pulverizinq Ini.ll Alternatively the signal representAtive of the meisllre(l carbon monoxide equivalent (COe) level which is transmit~d along line 24 may also provide an actuation of the alternate alarm 30 The measure-3 carbon monoxide equivalent (CO2) leve]
signal is transmitted to a derivative action controller 5() which is sensitive to any variations in the carbon monoxide equivalent (COe) level and provides an output signal alon~ a line 52 indicative of the slope or rate of change of the car-bon monoxide equivalent (COe) level in the pulverizing mill 1 The output of the derivative action controller 50 is trans-mitted along line 52 to a difference station 54 having a pre-determined setpoint providel along 2 line 56 r-presentative of a rate of change of the carbon monoxide equivalent (COe) level which wouli indicate coal ignition in the pulverizinq mill l~i 1;~691~
The output of the difference station 54 is transmitted alonq a line 58 to an ~ gate 60 having a second input ofa cOn-stant positive value provided alonq a line 62. In oc?eration, the rate of chanqe of the carbon monoxide equivalent (COr) level normAl.Ly stays below the setpoint applied to the ~lir-ference s~ation 54 resultinq in a negative output siqnal from this station 54 alonq line 58. ~henever the actual r~te of change of the carbon monoxicle equivalent (COe) level in the pulverizinq mill exceeds the setpoint provided alonq line 56 to this difference station 54, the signal transmitted along line 58 becomes positive, causing the AND gate 60 to concluct resulting in the transmission of a control siqnal alonq a line 64 to the alarm 8n actuating same to indicate the existence of a potentially dangerous condition in the pulveri%ing mill 14.
The foregoing alarms 28 and 30, when actuated, warn the operator of a potentially dangerous condition in the pulveriz-ing mill 14. These alarms should indicate to the operator that close monitoring of the pulverizing mill 14 is required and generally one al~rm will be actuated, possihly followecl by a second alarm. Since the inerting of the pulverizinq mill 14 may shock the pulverizer, such inerting is left to the discretion of the operator. There are, however, certnin conditions beyond which inerting of the pulverizinq mill 14 is mandatory and must be automatically initiated. To provide for such automatic inerting of the pulverizing mi.ll 14, the control system 10 again utilizes both the net oxygen (2~ measurements and the carbon monoxide equivalent (COe) measurements provided via lines 22 and 24, respectively.
~ utomatic inerting of the pulverizinq mill 14 is actuated by a difference station 66 which has a net oxygen level set-point provided to it along a line 68. The net oxygen level 5~
_9_ setpoint provided to the difference station 66 is signifi-cantly lower thall the setpoint level provided to the differ--ence station 38 Tllus ~luring normal operation of the p~
verizinq mill l4 the net o yqen (2~ level measured and transmittel to the difference station 66 will exceed thc setpoint applie(l thereto and the error signal pro~uced hy tlle differel~(e statioll 66 will be a positive signal which is transmitte~l aloncl a line 70 to an ~ND gate 72. The other in-put of tne ~N~ gate 72 is provided by a constant negativesignal along a line 74. Thus during normal operation of the pulverizinq mill 14 the inouts to the ~ qate 72 will he positive and negative resulting in no control signal be;nq transmitted froln the ~ND gate 72 alonq a line 76. Whenever the net oxyqen (2) level within the pulverizing mill 14 falls below the setpoint level applied to the ~ifference station 66 the output of this station 66 becomes negative providinq two negative inpu.s to the ~ND gate 72 resulting in the transllis-sion of a control signal along line 76 to a switching cir-cuit 78 The switclling circuit 78 is a normally open cir-cuit preventing the signal from a controller 80 from reach-ing the control valve 32. When a control siqnal is present along line 76 the switching circuit 78 changes to a closed circuit condition which results in the controller 80 beinq responsib]e for tle operation of the valve 32.
One inpl]t to the controller 80 is the actual net oxyg~n ~2) level in the pulverizing mill 14 and is provided by a line 82 which is connected to line 22. The setpoint for the con-troller 8n is provided along a line 84 from some setpoint sta-tion and tlle level of this setpoint is typically between t)esetpoint levels for difference stations 66 and 38. Thus when the switching circuit 78 is actuate~ by a control signal from the ~ND gate 72 in~iicating that the net oxygen (2) level within the pulverizing mill 14 has fallen below the set-point level to the ~ifference station 66 the controller 8n ~69~ jO
will open valve 32 causinq an inertinq atmosphere, such as carbon dioxide, to be delivered to the pulverizing mill 14 until a somewhat normal net oxYqen level is reached close to the setpoir-t ~evel for the controller 8n. Typica]ly, 1 he setpoint level for the controller 8n is kept some~hat lo-rer than normal atmosphere to minimize the shock to the pul~;er-izer 14 due to the inertinq process. When the net oxyqen (2) level in the pulverizing mill lq reaches the setpoint level for the controller 80, the .switching circuit 78 can then be reset to its normally open condition by a reset sigr)al along a line 86 from either a manual source or an automatic source tied to some parameter indicative of the establishment of normal operating conditions within the pulverizing mill 14.
The actuation of the automatic inertinq means is also alternatively done upon the sensing of a predetermined ahso-lute carbon monoxide equivalent (COe) level in the pulveriz-ing mill 14. The carbon monoxide equivalent (CO~) siqna~
normally provided on line 24 is tapped hy a line 88 to pro-vide one input to a difference station 90. The setpoint of the difference station 90 is provided alonq a line 92 from a setpoint station and the level of this setpoint ic typically set at the maximum carbon monoxide equivalent (COe) level which can he tolerated in the pulverizinq mill 14. Thus, as long as the carbon monoxide equivalent (COe) level stays below the setpoint for the difference station 90, a positive error signal will be transmitte~ by the dif-ference station sn along a line 9q to an ~ND gate 96. The other input to the ~ND gate 9fi is a constant negative siq-nal provided along a line 98. Thus, during normal operation
3() of the pulverizinq mill 14, opposite polarity signals are applied to the inputs to the ~ND gate 96, preventinq the transmission of any control signal alonq a line 100 from the AND gate 96. Whenever the absolute carbon monoxide equivalent 9~5() (COe) level exceeds the setpoint level applied to the Airfer-ence station 90 the error sigra] tr~nsmitted to the ~ qate 96 becomes negative causinq the conductioll of the ~1) 9a~e 96 and the establishment of a control signal alorlg line 1()() to the switching circuit 78. ~s was previously desc~ el Witll respect to the net oxygen 102) level control the fore-going causes the switching circuit 7B to be conAuctive turrl-inq control of the valve 32 over to the controller 80. ~n this manner automatic iner~.inq of the pulverizer 14 will occur until a reset signal is established along line 86.
causinq the switchinq circuit 78 to again become non-conductive and causing the valve to switch back to its normally closed position.
Oxygen fuel and an ignition source must be present in the pulverizing mill in order for A fire or explosion to occur.
The grinding of the coal in the pulverizinq mill releases hydrogen methane ethane and other combustible hydrocar!~or~.
Carbon monoxiAe is present only in very low levels durillq tlle 2Q grinding process unless the oxidation process has commence(~.
Once the oxidation process has commenced and the coal tempera-ture rises all of the foregoinq combustible gases will evolve and can be utilized as an indicator of a potential~y dangerous condition. Figure 3 shows the general relationship of the resultinq carbon monoxide equivalent ICOe~ level in the pulverizing mill to the various combustible qaseous components which comprise same versu.s increasinq coal temperature. As shown in this Figure measuring the agqregate of all these gaseous compone-lts produces a response that is significantly more pronounced than that based only upon carbon monoxide and eliminates the limitations resulting from relyinq on only one gas viz. carhon monoxide.
It has been found that most pulverizing mill fires are preceded by a significant increase in the carbon monoxide 1~i91~0 equivalellt (COe) level in the rnill. This increase appears to he caused by the oxidation of a srnall pocket of coal within the bowl or underbowl area Investiqatitns have shown that s ch pockets of oxitlizinq coal can exist for a Io~n perio(1 of tine within the mil] anl have the potential oF
igniting a rulawav fire at any time. Such pockets can o~: be detecte-l by using previous methods OT' detection hut can he detectel througil the use of the present invention as shown in Figure ~. This Pigure illustrates a fire that was pre-ceded by elevated carbon monoxide equivalent (COe) levels indicating tlt? presence of smoldering coal in the pulverizing mill. Approximately ten minutes after the start-up of the pulverizing mill the carbon monoxide equivalent (COe) level lS increased to 250 ppm; thirty minutes after the increase in the carbon monoxide equivalent (COe) level the oxygen (O~) level spiked down to 5~ and the mill temperature went out of control indicatinq the presence of a fire within the mi1~
The fire was quickly extinguished by increasinq the coa] feed however observation of sparks from the underbowl sectio verified that a fire had occurred and that coal was stil]
smoldering in the mill. The carbon monoxide equiva1en~-(COe) level then gradurlly decreased to approximately 35 I-pm over the next seven hours. This indicated that the smolder-ing coal qradually burned itself out however the potential for a second fire luring this period was indicated hy the hi~l carbon monoxide equivalent (COe) level ~ n example of a smoldering fire which did not ignite the pulverizinq mill is shown in Figure 5. ~s shown in this Fiq-ure approximately one-half hour after start-up of the mill the carbon monoxide equivalent (COe) level increased from 35 ppm to 225 ppm. The carbon monoxide equivalent (COe) level remained at this hiqh level and the net oxygen (2) level fell slightly from 17.75~ to 1~.75~. The carbon monoxide equivalent (COe) and net oxygen (2) levels then returned to their normal i9~
levels. ~nvestigation of the pu~verizing mill reveale-l a small quantity of coal smoldering in the mill for tllirty minutes. I`he quantity of smolderinq coa] was not larqe enough to ignite the mill.
From t:he fore~oinq it is apparent that monitoring the carhon monoxide eq~i~alen~ (COel level in the pulverizinq mill provides a significant~ ~rn~r~ved 1~ethod fo~ tlle ear~
detection of a potentially danqerous condition in the mill so that the necessary corrective measures can be taken to avert a fire or explosion in same. Such early detection is not possible with the detection methods previously avai]a~le.
In summary, Fiqure 6 illust~a~es the general relation-ship c~f the c~rhon m~noxide equivalent (COe) level, net oxvclen tO2) level, and pulverizer mill condition. The normal o~era-tinq band 5hows a general relationship between carhon monoxide equivalent (COe) level, net oxygen (2) level, and the type of coal used. As the percent volatile material iTl tT-e coa I
increases, so does the expected carbon monoxide (COe) equiva-lent level. As the percent moistureincreases, the net oxyqen(2) level will decrease due to resulting higher moisture levels in the pulverizing mill gases. Rises in the carhon monoxide equivalent (COe) level combined with a constant or dropping net oxygen (2~ level indicates a smoldering condi-tion with a potential for a pulverizer mill fire. Conversely,increasing carbon monoxide equivalent (COe) level indicates that the pulveri%ing mill is in a potentially explosive con-dition. From the foregoing, the value of measuring and deter-mininq the carbon monoxide equivalent (COe) level, in conjunc-tion with the net oxyqen (2) level, is apparent in determin-inq the onset of a potentially dangerous condition in the pulverizinq mill.
Certain modif~atiol)s and improvements will occur to 1~i91~
those skille(l in the art upon reading the foreqoinq. It sho~ e un(lerstoo~ that all such modificati~ns an~
provements have ~een deleted herein for the sake of con-cisenes~s and readal~iIity but are properly within the scopeof the followinq claims.
causinq the switchinq circuit 78 to again become non-conductive and causing the valve to switch back to its normally closed position.
Oxygen fuel and an ignition source must be present in the pulverizing mill in order for A fire or explosion to occur.
The grinding of the coal in the pulverizinq mill releases hydrogen methane ethane and other combustible hydrocar!~or~.
Carbon monoxiAe is present only in very low levels durillq tlle 2Q grinding process unless the oxidation process has commence(~.
Once the oxidation process has commenced and the coal tempera-ture rises all of the foregoinq combustible gases will evolve and can be utilized as an indicator of a potential~y dangerous condition. Figure 3 shows the general relationship of the resultinq carbon monoxide equivalent ICOe~ level in the pulverizing mill to the various combustible qaseous components which comprise same versu.s increasinq coal temperature. As shown in this Figure measuring the agqregate of all these gaseous compone-lts produces a response that is significantly more pronounced than that based only upon carbon monoxide and eliminates the limitations resulting from relyinq on only one gas viz. carhon monoxide.
It has been found that most pulverizing mill fires are preceded by a significant increase in the carbon monoxide 1~i91~0 equivalellt (COe) level in the rnill. This increase appears to he caused by the oxidation of a srnall pocket of coal within the bowl or underbowl area Investiqatitns have shown that s ch pockets of oxitlizinq coal can exist for a Io~n perio(1 of tine within the mil] anl have the potential oF
igniting a rulawav fire at any time. Such pockets can o~: be detecte-l by using previous methods OT' detection hut can he detectel througil the use of the present invention as shown in Figure ~. This Pigure illustrates a fire that was pre-ceded by elevated carbon monoxide equivalent (COe) levels indicating tlt? presence of smoldering coal in the pulverizing mill. Approximately ten minutes after the start-up of the pulverizing mill the carbon monoxide equivalent (COe) level lS increased to 250 ppm; thirty minutes after the increase in the carbon monoxide equivalent (COe) level the oxygen (O~) level spiked down to 5~ and the mill temperature went out of control indicatinq the presence of a fire within the mi1~
The fire was quickly extinguished by increasinq the coa] feed however observation of sparks from the underbowl sectio verified that a fire had occurred and that coal was stil]
smoldering in the mill. The carbon monoxide equiva1en~-(COe) level then gradurlly decreased to approximately 35 I-pm over the next seven hours. This indicated that the smolder-ing coal qradually burned itself out however the potential for a second fire luring this period was indicated hy the hi~l carbon monoxide equivalent (COe) level ~ n example of a smoldering fire which did not ignite the pulverizinq mill is shown in Figure 5. ~s shown in this Fiq-ure approximately one-half hour after start-up of the mill the carbon monoxide equivalent (COe) level increased from 35 ppm to 225 ppm. The carbon monoxide equivalent (COe) level remained at this hiqh level and the net oxygen (2) level fell slightly from 17.75~ to 1~.75~. The carbon monoxide equivalent (COe) and net oxygen (2) levels then returned to their normal i9~
levels. ~nvestigation of the pu~verizing mill reveale-l a small quantity of coal smoldering in the mill for tllirty minutes. I`he quantity of smolderinq coa] was not larqe enough to ignite the mill.
From t:he fore~oinq it is apparent that monitoring the carhon monoxide eq~i~alen~ (COel level in the pulverizinq mill provides a significant~ ~rn~r~ved 1~ethod fo~ tlle ear~
detection of a potentially danqerous condition in the mill so that the necessary corrective measures can be taken to avert a fire or explosion in same. Such early detection is not possible with the detection methods previously avai]a~le.
In summary, Fiqure 6 illust~a~es the general relation-ship c~f the c~rhon m~noxide equivalent (COe) level, net oxvclen tO2) level, and pulverizer mill condition. The normal o~era-tinq band 5hows a general relationship between carhon monoxide equivalent (COe) level, net oxygen (2) level, and the type of coal used. As the percent volatile material iTl tT-e coa I
increases, so does the expected carbon monoxide (COe) equiva-lent level. As the percent moistureincreases, the net oxyqen(2) level will decrease due to resulting higher moisture levels in the pulverizing mill gases. Rises in the carhon monoxide equivalent (COe) level combined with a constant or dropping net oxygen (2~ level indicates a smoldering condi-tion with a potential for a pulverizer mill fire. Conversely,increasing carbon monoxide equivalent (COe) level indicates that the pulveri%ing mill is in a potentially explosive con-dition. From the foregoing, the value of measuring and deter-mininq the carbon monoxide equivalent (COe) level, in conjunc-tion with the net oxyqen (2) level, is apparent in determin-inq the onset of a potentially dangerous condition in the pulverizinq mill.
Certain modif~atiol)s and improvements will occur to 1~i91~
those skille(l in the art upon reading the foreqoinq. It sho~ e un(lerstoo~ that all such modificati~ns an~
provements have ~een deleted herein for the sake of con-cisenes~s and readal~iIity but are properly within the scopeof the followinq claims.
Claims (12)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An improved safety system for a coal pulverizing mill comprising:
means for determining the rate of change of the level of carbon monoxide and other combustible gases in the coal pulverizing mill and establishing a signal indicative thereof;
means for comparing said signal from said determining means with a predetermined setpoint signal indicative of a potentially hazardous rate of change of the level of carbon monoxide and other combustible gases in the coal pulverizing mill and establishing a first control signal therefrom; and alarm means responsive to said first control signal for indicating a potentially hazardous condition in the coal pulverizing mill.
means for determining the rate of change of the level of carbon monoxide and other combustible gases in the coal pulverizing mill and establishing a signal indicative thereof;
means for comparing said signal from said determining means with a predetermined setpoint signal indicative of a potentially hazardous rate of change of the level of carbon monoxide and other combustible gases in the coal pulverizing mill and establishing a first control signal therefrom; and alarm means responsive to said first control signal for indicating a potentially hazardous condition in the coal pulverizing mill.
2. The improved safety system as defined in claim 1 further including:
means for measuring the level of carbon monoxide and other gases in the coal pulverizing mill; and a derivative action controller connected to said measur-ing means to provide an output signal indicative of the rate of change of the level of carbon monoxide and other combustible gases in the coal pulverizing mill.
means for measuring the level of carbon monoxide and other gases in the coal pulverizing mill; and a derivative action controller connected to said measur-ing means to provide an output signal indicative of the rate of change of the level of carbon monoxide and other combustible gases in the coal pulverizing mill.
3. The improved safety system as defined in claim 1 further including:
means for measuring the net oxygen level in the coal pulver-izing mill and establishing a signal indicative thereof; and means for comparing said signal from said net oxygen level measuring means with a first predetermined setpoint signal indicative of a potentially hazardous net oxygen level in the coal pulverizing mill and establishing a second con-trol signal therefrom;
said alarm means being responsive also to said second control signal.
means for measuring the net oxygen level in the coal pulver-izing mill and establishing a signal indicative thereof; and means for comparing said signal from said net oxygen level measuring means with a first predetermined setpoint signal indicative of a potentially hazardous net oxygen level in the coal pulverizing mill and establishing a second con-trol signal therefrom;
said alarm means being responsive also to said second control signal.
4. The safety system as defined in claim 3 further including:
means for comparing said signal from said net oxygen level measuring means with a second predetermined setpoint signal indicative of a potentially hazardous net oxygen level in the coal pulverizing mill and establishing a third control signal therefrom; and inerting means responsive to said third control signal for inerting the coal pulverizing mill.
means for comparing said signal from said net oxygen level measuring means with a second predetermined setpoint signal indicative of a potentially hazardous net oxygen level in the coal pulverizing mill and establishing a third control signal therefrom; and inerting means responsive to said third control signal for inerting the coal pulverizing mill.
5. The safety system as defined in claim 4 wherein said inerting means comprises:
a source of inerting atmosphere for inerting the coal pulverizing mill;
valve means for controlling said source of inerting atmosphere; and controller means being responsive to said third control signal for controlling said valve means.
a source of inerting atmosphere for inerting the coal pulverizing mill;
valve means for controlling said source of inerting atmosphere; and controller means being responsive to said third control signal for controlling said valve means.
6. The safety system as defined in claim 5 further including switching means being connected between said controller means and said valve means and being responsive to said third con-trol signal to allow control of said valve means by said controller means.
7. An improved safety system for a coal pulverizing mill comprising:
means for measuring the level of carbon monoxide and other gases in the coal pulverizing mill and establishing a signal indicative thereof;
means for comparing said signal from said measuring means with a predetermined setpoint signal indicative of a hazardous level of carbon monoxide and other combustible gases in the coal pulverizing mill and establishing a first-control signal therefrom; and inerting means responsive to said first control signal for inerting the coal pulverizing mill.
means for measuring the level of carbon monoxide and other gases in the coal pulverizing mill and establishing a signal indicative thereof;
means for comparing said signal from said measuring means with a predetermined setpoint signal indicative of a hazardous level of carbon monoxide and other combustible gases in the coal pulverizing mill and establishing a first-control signal therefrom; and inerting means responsive to said first control signal for inerting the coal pulverizing mill.
8. The improved safety system as defined in claim 7 where-in said inerting means comprises:
a source of inerting atmosphere for inerting the coal pulverizing mill;
valve means for controlling said source of inerting atmosphere; and controller means responsive to said first control sig-nal from said comparing means for controlling said valve means.
a source of inerting atmosphere for inerting the coal pulverizing mill;
valve means for controlling said source of inerting atmosphere; and controller means responsive to said first control sig-nal from said comparing means for controlling said valve means.
9. The improved safety system as defined in claim 8 further including:
means for measuring the net oxygen level in the coal pulverizing mill and establishing a signal indicative thereof;
means for comparing said signal from said net oxygen level measuring means with a first predetermined setpoint signal indicative of a potentially hazardous net oxygen level in the coal pulverizing mill and establishing a second con-trol signal therefrom; and alarm means responsive to said second control signal to indicate a potentially hazardous condition in the coal pulverizing mill.
means for measuring the net oxygen level in the coal pulverizing mill and establishing a signal indicative thereof;
means for comparing said signal from said net oxygen level measuring means with a first predetermined setpoint signal indicative of a potentially hazardous net oxygen level in the coal pulverizing mill and establishing a second con-trol signal therefrom; and alarm means responsive to said second control signal to indicate a potentially hazardous condition in the coal pulverizing mill.
10. The improved safety system as defined in claim 9 further including:
means for comparing said signal from said net oxygen level measuring means with a second predetermined setpoint signal lower than said first predetermined setpoint signal indicative of a potentially hazardous net oxygen level in the coal pulverizing mill and establishing a third control signal therefrom;
said controller means also being responsive to said third control signal for controlling said valve means.
means for comparing said signal from said net oxygen level measuring means with a second predetermined setpoint signal lower than said first predetermined setpoint signal indicative of a potentially hazardous net oxygen level in the coal pulverizing mill and establishing a third control signal therefrom;
said controller means also being responsive to said third control signal for controlling said valve means.
11. The improved safety system as defined in claim 10 fur-ther including switching means connected between said con-troller means and said valve means and being responsive to control signals from either said comparing means which com-pares the level of carbon monoxide and other combustible gases in the coal pulverizing mill with a predetermined set-point signal or said comparing means which compares the net oxygen level in the coal pulverizing mill with said second predetermined setpoint signal for allowing control of said valve means by said controller means.
12. A safety system for a coal pulverizing mill comprising:
means for measuring the net oxygen level in the coal pulverizing mill and establishing a signal indicative thereof;
means for determining the rate of change in the level of carbon monoxide and other combustible gases in the coal pulverizing mill and establishing a signal indicative thereof;
comparing means for comparing said signals established by said measuring means and said determining means with pre-determined setpoint signals for establishing independent control signals whenever the respective predetermined set-point signal is exceeded; and alarm means responsive to either of said independent control signals for indicating a potentially hazardous condi-tion in the coal pulverizing mill.
means for measuring the net oxygen level in the coal pulverizing mill and establishing a signal indicative thereof;
means for determining the rate of change in the level of carbon monoxide and other combustible gases in the coal pulverizing mill and establishing a signal indicative thereof;
comparing means for comparing said signals established by said measuring means and said determining means with pre-determined setpoint signals for establishing independent control signals whenever the respective predetermined set-point signal is exceeded; and alarm means responsive to either of said independent control signals for indicating a potentially hazardous condi-tion in the coal pulverizing mill.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US85770086A | 1986-04-29 | 1986-04-29 | |
| US857,700 | 1986-04-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1269150A true CA1269150A (en) | 1990-05-15 |
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ID=25326555
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000530556A Expired - Fee Related CA1269150A (en) | 1986-04-29 | 1987-02-25 | Apparatus and method for monitoring low-level combustibles |
Country Status (12)
| Country | Link |
|---|---|
| EP (1) | EP0244074B1 (en) |
| JP (1) | JPS62258759A (en) |
| KR (1) | KR950001974B1 (en) |
| AU (1) | AU591260B2 (en) |
| BR (1) | BR8702407A (en) |
| CA (1) | CA1269150A (en) |
| DE (1) | DE3765686D1 (en) |
| ES (1) | ES2018824B3 (en) |
| HK (1) | HK42692A (en) |
| IN (1) | IN166429B (en) |
| MX (1) | MX168789B (en) |
| SG (1) | SG36192G (en) |
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| CN104152196B (en) * | 2014-05-30 | 2016-06-29 | 中国石油化工股份有限公司青岛安全工程研究院 | The complete explosion-proof method of coal petrography oil device |
| CN106964474B (en) * | 2017-05-16 | 2018-04-20 | 安徽工业大学 | A kind of coal pulverizer explosive-proof test system |
| CN107797965A (en) * | 2017-10-23 | 2018-03-13 | 内蒙古岱海发电有限责任公司 | A kind of update method and system of pulverizer outlet temperature secure setting |
| CN112536145B (en) * | 2020-11-20 | 2022-06-21 | 西安热工研究院有限公司 | Medium-speed coal mill operation safety on-line monitoring and early warning system and method |
| CN115301391B (en) * | 2022-08-04 | 2023-12-15 | 中国能源建设集团西北电力试验研究院有限公司 | Intelligent control shutdown method for direct-blowing pulverizing system |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3237634A (en) * | 1966-03-01 | Process control system | ||
| US2799848A (en) * | 1953-12-17 | 1957-07-16 | Glantz Lester Murray | Two-level control system |
| US3912015A (en) * | 1974-06-17 | 1975-10-14 | Armco Steel Corp | System for the safe handling of pulverized coal |
| GB1485448A (en) * | 1974-11-11 | 1977-09-14 | Boc International Ltd | Comminuting combustible material |
| US4031747A (en) * | 1976-08-16 | 1977-06-28 | Beckman Instruments, Inc. | Misfire monitor for engine analysis having automatic rescaling |
| JPS5820247A (en) * | 1981-07-30 | 1983-02-05 | バブコツク日立株式会社 | Detection of ignition in mill |
| KR900002655B1 (en) * | 1983-08-01 | 1990-04-21 | 더 뱁콕 앤드 윌콕스 컴퍼니 | Safety system for coal pulverizers |
| JPS6094154A (en) * | 1983-10-28 | 1985-05-27 | 三菱重工業株式会社 | Explosion-proof coarse garbage crusher |
-
1986
- 1986-11-14 IN IN823/CAL/86A patent/IN166429B/en unknown
- 1986-12-24 KR KR1019860011219A patent/KR950001974B1/en not_active IP Right Cessation
-
1987
- 1987-02-25 CA CA000530556A patent/CA1269150A/en not_active Expired - Fee Related
- 1987-03-17 DE DE8787302255T patent/DE3765686D1/en not_active Expired - Fee Related
- 1987-03-17 ES ES87302255T patent/ES2018824B3/en not_active Expired - Lifetime
- 1987-03-17 EP EP87302255A patent/EP0244074B1/en not_active Expired - Lifetime
- 1987-04-03 AU AU71063/87A patent/AU591260B2/en not_active Ceased
- 1987-04-28 JP JP62103439A patent/JPS62258759A/en active Pending
- 1987-04-29 MX MX006272A patent/MX168789B/en unknown
- 1987-04-29 BR BR8702407A patent/BR8702407A/en unknown
-
1992
- 1992-03-31 SG SG361/92A patent/SG36192G/en unknown
- 1992-06-11 HK HK426/92A patent/HK42692A/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| SG36192G (en) | 1992-05-22 |
| AU591260B2 (en) | 1989-11-30 |
| AU7106387A (en) | 1987-11-05 |
| ES2018824B3 (en) | 1991-05-16 |
| KR950001974B1 (en) | 1995-03-08 |
| KR870010430A (en) | 1987-11-30 |
| IN166429B (en) | 1990-05-05 |
| EP0244074B1 (en) | 1990-10-24 |
| EP0244074A2 (en) | 1987-11-04 |
| HK42692A (en) | 1992-06-19 |
| JPS62258759A (en) | 1987-11-11 |
| DE3765686D1 (en) | 1990-11-29 |
| EP0244074A3 (en) | 1988-08-10 |
| BR8702407A (en) | 1988-02-17 |
| MX168789B (en) | 1993-06-08 |
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Legal Events
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| MKLA | Lapsed |