CN109357424B - Process and method for reducing propylene consumption of propylene refrigeration system - Google Patents

Abstract

The invention provides a process and a technology for reducing propylene consumption of a propylene refrigeration system, and the process comprises a start stage working section and an operation stage working section, wherein: the start-up stage section comprises a propylene buffer tank, a propylene evaporator and a propylene superheater which are sequentially communicated, and the propylene superheater is communicated with a dry gas sealing device; the operation stage section comprises a propylene evaporator, and a liquid inlet and a gas outlet of the propylene evaporator are respectively communicated with the first-stage separator. The invention reduces the permanent operation cost in the operation process by increasing the one-time equipment investment, and can save the production cost for enterprises, thereby generating economic benefits for the enterprises.

Description

Process and method for reducing propylene consumption of propylene refrigeration system

Technical Field

The invention belongs to the field of propylene refrigeration systems, and particularly relates to a process for reducing propylene consumption of a propylene refrigeration system.

Background

The propylene refrigeration system provides cold energy for a coal chemical industry low-temperature methanol washing device, an MTO olefin separation device and the like. The propylene refrigeration system compresses low-temperature and low-pressure propylene gas by using a centrifugal compressor, cools the propylene gas to a liquid phase by using circulating water, sends the propylene gas to a downstream device after being supercooled, and provides cold energy for the device by propylene evaporation.

The conventional flow of a propylene refrigeration system is shown in a figure 1, and the specific process flow is illustrated as follows:

gaseous propylene (0.04MPaG, -40 ℃) from a cold device enters a first-section inlet separator (V001) of a propylene compressor, after entrained liquid drops are separated, a gas phase enters a first-section inlet separator of the compressor, and a liquid phase of the first-section inlet separator is directly discharged to a torch or discharged to a propylene buffer tank (V003) by a propylene pump; the outlet pressure of the first section of the compressor is 0.55MPaG, the propylene gas at the outlet of the first section and the gas phase of the power economizer (V004) enter a second-section inlet separator (V002), the gas phase enters the second section of the compressor after entrained liquid drops are separated out, and the liquid phase is discharged to the first-section inlet separator; the pressure of the second-stage outlet of the compressor is 1.7MPaG, the propylene gas at the second-stage outlet is condensed into 40 ℃ liquid propylene by a propylene cooler (E001) and a propylene condenser (E002), the liquid propylene enters a power economizer with the pressure of 0.55MPaG after passing through a propylene buffer tank, the gas phase is used as the second-stage air supplement of the compressor, the liquid phase is divided into two parts, one part enters a shell pass of a propylene subcooler (E003), the other part enters a propylene subcooler tube pass, the shell pass propylene is decompressed to 0.04MPaG, the temperature is reduced to-40 ℃, the propylene in the shell pass evaporates and absorbs heat to reduce the temperature of the tube pass propylene, the temperature of the tube pass propylene is reduced to-20 ℃, and the pressure of the subcooled propylene in the process is 0.55MPaG, and the temperature is reduced to-20 ℃ and is sent to a downstream cold working section.

Superheated propylene gas at the outlet of the second section of the compressor is used as primary isolation gas for dry gas sealing, and nitrogen of 3.0MPaG is used as primary sealing gas for dry gas sealing in the starting stage.

The propylene refrigeration system is relatively mature, but the large propylene loss is always a problem troubling enterprises, and the propylene loss of the propylene refrigeration system is caused by the following reasons:

firstly, the method comprises the following steps: at the start-up stage, can't use the process gas as the primary seal gas, can only adopt 3.0MPaG even higher pressure nitrogen as the primary seal gas, just introduce the dry gas seal as the primary seal gas after the process gas forms the high pressure, if this process of the start-up is not smooth can last more than 24 hours, lead to a large amount of noncondensable gas to get into the system, discharge noncondensable gas through the mode of discharging the torch, noncondensable gas smugglies a large amount of propylene simultaneously and discharges to the torch, take 80 ten thousand tons of methyl alcohol projects of annual output as an example, because noncondensable gas discharges the torch and can have the propylene of probably more than 60 tons to discharge to the torch, calculate with propylene price 8000 yuan per ton, direct economic loss is nearly 50 ten thousand yuan.

Secondly, the method comprises the following steps: a small amount of non-condensable gas passes through the non-condensable gas cooler in the normal operation process, propylene returns to the system, the non-condensable gas is discharged to a torch, and the propylene is leaked to the torch due to the unreasonable design of the non-condensable gas cooler, so that propylene loss is caused.

Thirdly, the method comprises the following steps: the first-stage separator and the second-stage separator do not carry out liquid phase operation as far as possible in the normal operation process, otherwise, the inlet of the compressor is carried with liquid, so that the compressor jumps, but the liquid phase of the separator is inevitably generated in the starting and stopping process and the normal operation process, the liquid phase of the second-stage separator is discharged to the first-stage inlet separator through the liquid level regulating valve, and after the liquid level of the first-stage inlet separator is high, two conventional means are adopted at present:

firstly, the method comprises the following steps: directly discharged to a torch, thereby causing the waste of propylene liquid;

II, secondly: the propylene shield pump is used for boosting pressure and then is discharged to the propylene buffer tank, but the shield pump is very easy to generate cavitation by the method, so that the shield pump cannot be put into use.

Disclosure of Invention

The novel process for reducing the propylene consumption is provided for solving the problem of serious propylene loss of a propylene refrigeration system, the permanent operation cost in the operation process is reduced by increasing the one-time equipment investment, the production cost can be saved for enterprises, and the economic benefit is generated for the enterprises.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

a process for reducing propylene consumption in a propylene refrigeration system comprising a start-up phase section and an operating phase section, wherein:

the start-up stage section comprises a propylene buffer tank, a propylene evaporator and a propylene superheater which are sequentially communicated, and the propylene superheater is communicated with a dry gas sealing device;

the operation stage section comprises a propylene evaporator, and a liquid inlet and a gas outlet of the propylene evaporator are respectively communicated with the first-stage separator.

Further, the process also comprises a non-condensable gas treatment system, and the non-condensable gas treatment system comprises a non-condensable gas cooler.

Further, the propylene evaporator was heated by a water bath heater.

Further, the start-up stage section and the operation stage section share one propylene buffer tank.

The invention also aims to provide a process method for reducing the propylene consumption of a propylene refrigeration system, which comprises the following steps:

step 1, operating the start-up stage section during start-up, and closing the operation stage section;

step 2, closing the start-up stage workshop section and opening the operation stage workshop section during operation;

and 3, treating the non-condensable gas by using the non-condensable gas treatment system.

Further, the step 1 specifically includes the following operation processes: and propylene in the propylene buffer tank enters the propylene evaporator, the propylene evaporator is heated by the water bath heater and generates saturated high-pressure propylene gas, the pressure of the propylene evaporator is controlled to be 1.5-1.6 MPaG, the temperature of the high-pressure propylene gas is 30-40 ℃, the propylene evaporator is overheated to 90-95 ℃ by the propylene superheater, and the overheated propylene gas enters dry gas for sealing use.

Further, the step 2 specifically includes the following operation processes: and closing the valve of the working section at the start-up stage, controlling the pressure of the propylene evaporator to be 0.04-0.1 MPaG, feeding the propylene liquid of the first-section inlet separator into the propylene evaporator, heating the propylene liquid by the water bath heater, gasifying the propylene liquid at the temperature of-40 to-30 ℃ and the pressure of 0.04-0.1 MPaG, returning the saturated gas to the first-section inlet separator, and feeding the saturated gas into the first section of the compressor.

Further, the step 3 specifically includes the following operation processes: the non-condensable gas from the propylene condenser enters the tube pass of the non-condensable gas cooler from the top of the non-condensable gas cooler, is divided into a gas phase and a liquid phase after being cooled by the shell pass of the non-condensable gas cooler, the gas phase is decompressed by a pressure regulating valve and then discharged to a torch system, and the liquid phase is discharged to the propylene buffer tank under the action of gravity;

the shell pass of the non-condensable gas cooler is liquid propylene from the propylene buffer tank, the propylene on the tube pass of the non-condensable gas cooler is cooled through the evaporation and heat absorption of the propylene on the shell pass of the non-condensable gas cooler, and the gas phase of the shell pass of the non-condensable gas cooler returns to the first-stage inlet separator.

Compared with the prior art, the invention has the following advantages:

(1) the start-up stage section adopts a new process to provide overheated high-pressure propylene gas for dry gas sealing, avoids using medium-pressure nitrogen gas, can avoid non-condensable gas from leaking into a system, and reduces the loss of propylene in the non-condensable gas discharging process;

(2) the operation stage section adopts a new process to discharge propylene liquid to the propylene evaporator, and the propylene liquid returns to the system after being heated and evaporated by the water bath heater, so that waste caused by discharging into a torch is avoided.

(3) The non-condensable gas cooler is designed to be inclined, and cooled gas-liquid two phases are separated in the tube pass tube box, so that the cooling effect can be improved, and the loss of propylene can be reduced.

(4) The mode that adopts water bath heater heats gasification propylene, and the temperature is easily controlled, and the superpressure is difficult to the propylene vaporizer, compares in addition in the heat exchanger of BKU formula and can solve the stifled problem of tube side freeze.

(5) After water for the water bath heater comes from a steam turbine condensate pump, once the propylene evaporator has liquid propylene and the water bath heater is low in liquid level, the control valve can be opened through liquid level control to supplement hot condensate, and the liquid propylene is rapidly evaporated.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the invention without limitation. In the drawings:

FIG. 1 is a schematic diagram of a conventional flow scheme for a propylene refrigeration system;

fig. 2 is a schematic process flow diagram of an embodiment of the present invention.

Description of reference numerals:

v001-first stage inlet separator; v002-two-stage inlet separator; a V003-propylene buffer tank; v004-power saver; v005-propylene evaporator; V006-Water tank;

a C001-propylene compressor;

an E001-propylene chiller; e002-propylene condenser; e003-propylene subcooler; e004-noncondensable gas cooler; e005-water bath heater; e006-propylene superheater.

Detailed Description

It should be noted that the embodiments and features of the embodiments of the present invention may be combined with each other without conflict.

In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like are used in the orientation or positional relationship indicated in the drawings, which are merely for convenience in describing the invention and to simplify the description, and are not intended to indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be construed as limiting the invention. Furthermore, the terms "first", "second", etc. are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first," "second," etc. may explicitly or implicitly include one or more of that feature. In the description of the invention, the meaning of "a plurality" is two or more unless otherwise specified.

In the description of the invention, it is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted", "connected" and "connected" are to be construed broadly, e.g. as being fixed or detachable or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the creation of the present invention can be understood by those of ordinary skill in the art through specific situations.

The invention will be described in detail with reference to the following embodiments with reference to the attached drawings.

The process flow of the invention is as follows:

firstly, driving working conditions;

propylene 06 (pressure 1.7MPaG, temperature 40 ℃) in a propylene buffer tank (V003) can enter a propylene evaporator (V005) in a start-up stage, the propylene evaporator is heated by a water bath heater (E005), the temperature in the water bath heater is controlled at 60 ℃, saturated high-pressure propylene gas 07 is generated, the pressure of the propylene evaporator is controlled at 1.5-1.6 MPaG, the temperature of the high-pressure propylene gas 07 is 30-40 ℃, the propylene gas is superheated to 90-95 ℃ through a propylene superheater (E006), and superheated propylene gas 08 enters dry gas for sealing use. Therefore, the compressor can be started without using medium-pressure nitrogen, and the accumulation of non-condensable gas in a system is avoided, so that the consumption loss of propylene is reduced.

Secondly, normal working conditions are carried out;

after the propylene refrigeration system is started, the valve V3 and the valve V9 can be closed, the valve V7 is opened, the pressure of a propylene evaporator (V005) is controlled to be 0.04-0.1 MPaG, propylene liquid 13 in a first-stage inlet separator enters the propylene evaporator, is gasified after being heated by a water bath heater, the temperature of saturated gas is-40 to-30 ℃, and the pressure is 0.04-0.1 MPaG, and then the saturated gas returns to the first-stage inlet separator and enters a first stage of a compressor. Thereby the propylene liquid of the first-stage inlet separator is recycled to the system, and the waste caused by discharging the propylene into a torch is avoided.

The non-condensable gas in the system is mainly concentrated in a propylene condenser, the non-condensable gas 04 (with the temperature of 40 ℃ and the pressure of 1.7 MPaG) from the propylene condenser enters the tube pass of the propylene condenser from the top of a non-condensable gas cooler (E004), the non-condensable gas is divided into a gas phase and a liquid phase after being cooled by the shell pass of the non-condensable gas cooler, the gas phase 05 is decompressed by a pressure regulating valve V2 and then discharged to a torch system, and the liquid phase 02 is discharged to a propylene buffer tank under the action of gravity. The shell pass of the non-condensable gas cooler is that liquid propylene 01 from a propylene buffer tank is decompressed through a valve V1, the temperature is reduced to-40 ℃, the liquid propylene enters the shell pass of the non-condensable gas cooler, the propylene in the tube pass is cooled through the evaporation and heat absorption of the propylene in the shell pass, and the gas phase 03 in the shell pass returns to the first-stage inlet separator. The non-condensable gas cooler is arranged at 45 ℃ in an inclined mode, the cooled non-condensable gas is subjected to gas-liquid separation at a pipe box at the bottom of the non-condensable gas cooler, and the heat exchange effect can be improved due to the fact that a pipe side and a shell side are in countercurrent. The conventional non-condensable gas cooler is vertical, the flow directions of the non-condensable gas on the tube pass and the condensed propylene are opposite, the resistance of the non-condensable gas cooler is increased, and the cooling effect is reduced.

Thirdly, key equipment;

1. a propylene evaporator and a water bath heater;

the propylene evaporator and the water area heating pot are integrated equipment, the water bath heating pot is heated by low-pressure steam, the opening degree of the V10 is controlled by the pressure of the propylene evaporator to adjust the pressure, and the valve V5 is automatically opened to automatically supplement condensate from a condensate pipeline of the steam turbine after the liquid level of the water bath heating pot is lower than a normal value.

The water bath heater sets up coil pipe heating in the low pressure steam, has set up overflow line 15 simultaneously, and after the liquid level height, the condensate passes through overflow line and arranges to the trench, protection equipment.

Meanwhile, the water bath heater is provided with an exhaust pipeline 17, a water tank (V005) is arranged for preventing water vapor at 60 ℃ from being directly exhausted to the atmosphere, the pipeline 17 is directly inserted below the page of the water tank, the water temperature of the water tank is normal temperature, the water vapor is cooled to be below 40 ℃, and the water vapor is directly exhausted to the atmosphere through an exhaust pipeline 18.

The design pressure and the design temperature of the propylene evaporator are-50/50 ℃ and 2.2MPaG respectively, and the water bath heater is a normal pressure device.

2. A propylene superheater;

the propylene superheater adopts low-pressure steam for heating, and the temperature of propylene at the outlet of the propylene superheater controls the opening degree of a low-pressure steam feeding valve V11, so that the outlet temperature is adjusted, and the propylene gas can enter dry gas for sealing after being superheated.

Example 1 was carried out: operating mode

In the starting process, liquid high-pressure propylene is injected into a propylene buffer tank from a propylene tank area, the pressure of the liquid propylene in the buffer tank is 1.8MPaG, the temperature is 40 ℃, the pressure is reduced to 1.5-1.6 MPaG through a pressure reducing valve, the pressure of a propylene evaporator is controlled to be 1.5-1.6 MPaG, the opening degree of an inner coil steam valve is controlled through the pressure of the propylene evaporator, saturated propylene gas enters a propylene superheater again, the propylene is heated to 90-95 ℃ by low-pressure steam, superheated propylene gas enters dry gas for sealing use, after the system is started, the pressure of the system is gradually increased, an outlet valve of the propylene evaporator is closed, and the superheated propylene at the outlet of a propylene compressor is switched to be used as primary isolation gas of the dry gas seal.

Example 2 was carried out: normal operating conditions

In the normal operation process, liquid propylene in the first-stage inlet separator is discharged into a propylene evaporator, steam is used for heating condensed water, the temperature of the condensed water is controlled to be 60 ℃, the condensed water is used for heating the liquid propylene, the temperature of the propylene evaporator is controlled to be-40 ℃, the pressure is controlled to be 0.04-0.1 MPaG, and evaporated gas propylene returns to the first-stage inlet separator.

EXAMPLE 3

The method comprises the steps that non-condensable gas with the pressure of 1.6-1.7 MPaG and the temperature of 40 ℃ from a condenser enters a tube pass of a non-condensable gas cooler, is cooled by propylene gas with the shell pass of-40 ℃ and the temperature of 0.04MPaG, is subjected to gas-liquid separation at a tube box at the bottom of the non-condensable gas cooler, a gas phase is discharged to a torch through a pressure regulating valve, a liquid phase returns to a propylene buffer tank, the pressure of the tube pass is controlled to be about 1.6MPaG, the non-condensable gas cooler is arranged in an inclined mode at 45 degrees, and condensed propylene liquid and the propylene gas flow in parallel, so that the resistance of the tube pass is reduced, and the cooling effect is improved.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be taken as limiting the invention, so that any modifications, equivalents, improvements and the like, which are within the spirit and principle of the present invention, should be included in the scope of the present invention.

Claims (5)

1. A process for reducing propylene consumption of a propylene refrigeration system is characterized in that: including driving stage workshop section and operation stage workshop section, wherein:

the start-up stage section comprises a propylene buffer tank, a propylene evaporator and a propylene superheater which are sequentially communicated, and the propylene superheater is communicated with a dry gas sealing device;

the operation stage section comprises a propylene evaporator, and a liquid inlet and a gas outlet of the propylene evaporator are respectively communicated with the first-stage inlet separator;

the process comprises the following steps:

step 1, operating the start-up stage section during start-up, and closing the operation stage section;

step 2, closing the start-up stage workshop section and opening the operation stage workshop section during operation;

the step 1 specifically comprises the following operation processes: and propylene in the propylene buffer tank enters the propylene evaporator, the propylene evaporator is heated by a water bath heater and generates saturated high-pressure propylene gas, the pressure of the propylene evaporator is controlled to be 1.5-1.6 MPaG, the temperature of the high-pressure propylene gas is 30-40 ℃, the propylene evaporator is overheated to 90-95 ℃ by the propylene superheater, and the overheated propylene gas enters dry gas for sealing use.

2. The process of claim 1 for reducing propylene consumption in a propylene refrigeration system, wherein: the process also comprises a non-condensable gas treatment system, wherein the non-condensable gas treatment system comprises a non-condensable gas cooler, and the non-condensable gas cooler is arranged at an inclination of 45 ℃.

3. The process of claim 1 for reducing propylene consumption in a propylene refrigeration system, wherein: the start-up stage workshop section and the operation stage workshop section share one propylene buffer tank.

4. The process of claim 1 for reducing propylene consumption in a propylene refrigeration system, wherein: the step 2 specifically comprises the following operation processes: and closing the valve of the working section at the start-up stage, controlling the pressure of the propylene evaporator to be 0.04-0.1 MPaG, feeding the propylene liquid of the first-section inlet separator into the propylene evaporator, heating the propylene liquid by the water bath heater, gasifying the propylene liquid at the temperature of-40 to-30 ℃ and the pressure of 0.04-0.1 MPaG, returning the saturated gas to the first-section inlet separator, and feeding the saturated gas into the first section of the compressor.

5. The process of claim 2 for reducing propylene consumption in a propylene refrigeration system, wherein: the process also comprises a step 3 of treating the non-condensable gas by using the non-condensable gas treatment system;

the step 3 specifically comprises the following operation processes: the non-condensable gas from the propylene condenser enters the tube pass of the non-condensable gas cooler from the top of the non-condensable gas cooler, is divided into a gas phase and a liquid phase after being cooled by the shell pass of the non-condensable gas cooler, the gas phase is decompressed by a pressure regulating valve and then discharged to a torch system, and the liquid phase is discharged to the propylene buffer tank under the action of gravity;

the shell pass of the non-condensable gas cooler is liquid propylene from the propylene buffer tank, the propylene on the tube pass of the non-condensable gas cooler is cooled through the evaporation and heat absorption of the propylene on the shell pass of the non-condensable gas cooler, and the gas phase of the shell pass of the non-condensable gas cooler returns to the first-stage inlet separator.

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