US1731315A - Method of and means for controlling the temperature of drying chambers - Google Patents

Description

0a. 15, 1929. M. L. MUELLER 133L3 METHOD OF AND MEANS FOR CONTROLLII JG THE TEMPERATURE OF DRYING CHAMBERS F116;; Feb. 2a. 1928 INVENTOR. Marv izl 27/1/8226 r ATTORNEYJ Patented Oct. 15, 1929 UNITED STATES PATENT OFFICE MORITZ L. MUELLER, OF SEATTLE, WASHINGTON, ASSIGNOR TO NORTHWEST BLOWER KILN COMPANY, OF PORTLAND, OREGON, A CORPORATION OF WASHINGTON METHOD OF AND MEANS FOR CONTROLLING THE TEMPERATURE OF DRYING CHAMBERS Application filed Februaly 28, 1928. Serial No. 257,688.

This invention relates to a method of and means for controlling the temperature of drying chambers, and more particularly for controlling the temperatures in lumber drying kilns, and its objectis to provide improvements in this art by means of which more uniform and effective results can be obtained, than is possible under existing methods. Many of the lumber drying kilns in use employ very long banks of steam coils, the steam to which is under control of a single automatic valve. The result is that when the automatic valve throttles the steam, one end of the kiln becomes hotter than the other, the steam admitted being insuificient to maintain a full head of steam at both ends of the coil. It is manifest that this produces a detrimental condition in the kiln, because the rate of drying of the material at one end of the kiln. will be faster than at the other end of the kiln.

Since steam radiation for all kilns must be installed in sufficient quantity to heat up the chamber and its contents from a cold condition, in a reasonable length of time, and also to supply heat for evaporation, it follows that after the kiln and its contents become heated there is a surplus of radiation. An excess of radiation is undesirable, because it produces the following detrimental results First: It causes uneven heating, as previously described. That is, it produces a condition wherein one end of the kiln is hotter than the other.

Second: Poor steam trap action results from the reduction of steam pressure in the 1 .coils. When the steam pressure is too low eflicient trap action cannot be had, and if the amount of radiation is excessive it follows that only a low pressure in the coils is necessary to create the desired temperature, and, as before stated, the steam traps will notoperate properly if the pressure is unduly low. Third: Excessive surging in the steam mains and boilers is caused by the high velocities of the steam, which are caused by excessive capacity ofthe radiating units. .This, in turn, causes excessive wear on the radiation and piping.

To obviate the foregoing difficulties, I divide the radiation into a plurality of units,

and provide each of these units with an automatic control valve for its steam supply, said, control valves being set to operate at differ ent temperatures, and all of the steam control valves being under the control of a master controller that is, in turn, under the control of the heat conditions in the drying chamber.

In the accompanying drawing:

Fig. 1 is a diagrannnatic view of one form of controlling mechanism, wherein the steam valves are opened under air pressure, and closed under the action of a spring, and

Fig. 2 is a like View, but with the parts so arranged that the steam valves are. closed under air pressure, and are opened under spring action.

In the drawing, 5 designates a drying chamher, and 6 and 7 designate separate steam coils therein. I preferably extend these coils substantially the full length of the drying chamber. The steam supply line 8, for coil 6, is controlled by a steam valve 9, While the steam supply line 10 for coil 7 is controlled by a valve 11. The stems of these valves are connected to flexible diaphragms 9 and 11*, and springs 12 and 13 tend t; move the stems of the valves upwardly. Fluid under pressure. such as compressed air, for example, from a fluid pressure supply line 14, is delivered through branches 15 and 16 to the upper sides of the diaphragms. Gauges 17 and 18 are disposed in the branches 15 and 16. The pressure fluid from pipe 14 is controlled by a valve 19. A heat control bulb 20 is connected by conduit 21 with an expansible element 22. In the form of the invention illustrated in Fig. 1, rise of temperature beyond a set point in chamber 5 acts through the heat control bulb and its connection 21, to expand element 29., and move a lever 23 upon its pivot 24 to move valve 19 in proportion to the degree the temperature pressure from the bulb exceeds the desired set temperature. For example, when the temperature in the drying chamber is much lower than the desired point, air valve 19 opens wide and puts full air pressure on the diaphragm 9, thereby opening the steam valve to a corresponding extent. Upon the other hand, when the ten'iperature of the kiln is close to the desired temperature, valve 19 opens only slightly, permitting but a low air pressure to be exerted against diaphragm 9 with a correspondingly small opening of the steam valve 9. When valve 19 closes, under the rise of temperature in the heating chamber, the air supply is cut oil from the dia phragms, and the springs 12 and 13 respondingly close the steam valves.

It isnotto, be understood that-the cutting off of the steam to coils 6 and 7 takes place simultaneously. Upon the contrary, the action of the valves 9 and 11 is a successive one. It is clear that the time of movement of these Valves is determined by the area of the diaphragms, Qfl'll", and the tension of springs 12 and 13. For example, a small efliective. diaphragm area and high spring tension will resultin operation of the steam valve only when the air pressure acting upon the diaphragm is relatively high, and, consequently, only when the action of the heat control bulb and its associated expan'sible element 22 has been a considerable one. Upon the other hand, a large effective diaphragm area, and a low spring compression will re- .sult in operation of the steam valve, at lower air pressures and, consequently, when only a slight change in heat'conditions in the drying chamber has acted upon the heat control bulb and its associated elements to shift the valve 19 but little, with a corresponding admissionof but a limited air pressure to the surface of the diaphragm.

Consequently,it will be seen that by the proper setting of the tension of the springs, in proportion to the diaphragm area, the steam valves may he made to open at some what'widely different points in the fluctuation of the temperature in the drying chamher.

I prefer to have these elements so adjusted that the control Valve of coil 7 opens up only to heat up the kiln at the start, or

to give the heat necessary for some radical change of temperature desired by the operator. Coils 6 are sufiicient to maintain the temperature once the kiln and its contents are heated up, and these coils maintain the temperature by going on and oii, under control of the bulb 20, under minor variations in the temperature, without the coil 7 coming into action at all, under normal conditions. The reduced radiation capacity represented by the coils 6, as compared with the total radiation capacity represented by both of the coils, results in the steam flowing evenly at'moderate velocity throughout the length of the coils 6, maintaining uniform 1lieating conditions from end to end of the iln.

The structure illustrated in Fig. 2 is suhstantially like that illustrated in Fig. 1, differing therefrom only in the disposition of the valves 9, 11, with. respect to their seats, and the manner of connecting the expansible element 22 with the air control valve 19.

act to corditions existing in the kiln.

2. The combination pands it tends to open valve 19, and admit more pressure from the air line to the diaphragms. This pressure acts against the springs to seat the valves, whereas in Fig. 1

the air pressure acts to unseat the valves, said valves being seated by the springs. However, the principle of operation is the same in each case, in so .tar as the provision of a plurality of steam coils, individually controlled by drying chamber conditions, and set for operation at radically different points in such drying chamber conditions, so that while both coils will be put in action when the kiln is 'started and until it and its contents are heated up, one of said coils will be automatically cut out of action after the kiln has heated up, and the other coil will thereafter be alternatel out off and on to maintain uniform drylng conditions throughout the length of the kiln.

While, for purposes of illustration, I have shown and described two coils, it is clear that any desired number of coils may be employed with an individual controller for I each, set to operate at different points in the tern erature variation in the drying chamber. eat control bulbs and expansible elements actuated thereby have acquired a distinct status in the art, and are well known in the lumber drying art. Consequently, these elements need no further description.

It is to be understood that this invention is not limited to the precise construction set forth, but that it includes within its purview Whatever changes fairly come Within either claims.

Having claim is: I

1. The herein described method of controlling the temperature of a lumber drying kiln, which consists of utilizing large capacity radiation throughout the length of the kiln until the .kiln and its contents are heated, and then automatically cutting out part of described my invention, what I said radiation throughout the length of the kiln and maintaining ture by the automatic control of the remainder of the radiation throughout the length of the kiln under the influence of the heat conelongated lumber drying chamber, and a plurality of radiating units therein each extending substantially the full length of the of individual automatic controllers for the tempera set for operation at difwithin the kiln.

kiln, each of said units operated by ture within the kiln, ferent temperatures the desired temperawith a horizontally 3. The combination with a horizontally elongated lumber drying chamber, and a plurality of steam radiating coils therein each extending substantially the full length of the kiln, of individual automatic controllers for each of said coils, set for operation at different temperatures Within the kiln, and a masher controller operated by temperature changes in the kiln for controlling the first named controllers.

4. The combination with a horizontally elongated lumber drying chamber, of a plurality of steam radiating coils therein each extending substantially the full length of the kiln, a steam supply line for each of said coils, an individual steam control valve for each line, a pressure operated member for actuating each steam valve, a fluid pressure supply line for supplying fluid to operate said valves, a controlling valve in the fluid pressure supply line, and an element acutated by temperature changes in the drying chamber for shifting the last named valve in proportion to the degree of such changes.

5. The combination with a' horizontally elongated lumber drying chamber, of a plurality of steam heating coils therein each extending substantially the full length of the kiln, an individual steam supply line for each of said coils, an individual steam valve for each of said lines, a pressure operated element connected to each of said steam valves, a fluid pressure supply line for delivering pressure fluid to each of said pressure operated elements, a controlling valve in the fluid pressure supply line, an expansible element for actuating said valve, a heat control bulb in the drying chamber, and a connection between the heat control bulb and the expansible element.

6. The combination with a drying chamber, of a pair of independent steam heating coils therein, one of which, at least, is substantially co-extensive with the length of the drying chamber, independent controlling means for controlling steam to each of said coils, said controlling means being under the control of the temperature in the kiln, one of said coils being of such capacity as to maintain the desired temperature in the kiln after the kiln and contents have once becomeheated, said controlling elements being so set that the other of said coils is brought into action I only when abnormal temperature changes are necessary, the controlling member of the last named coil serving to automatically out the same out of action and maintain it out of action after the kiln and contents become initially heated, the temperature in the kiln thereafter being maintained by the periodical automatic cutting into action of the first named coil.

7 The combination with a single chamber kiln, of a plurality of heating elements therein, an individual controlling member for each of said heating elements, pressure operated means for actuating said controlling members, set to operate at diflerent pressures, a. fluid pressure supply line in communication with said pressure operated means, a valve for controlling the flow of pressure fluid in said line, a temperature controlled element in the kiln, and a member acting under the control of said pressure operated means to move the control valve of the pressure su ply line successively to positions to bring a out the operation of first one and then the other of such pressure controlled means.

In testimony whereof I aflix my signature.

k MORITZ .L. MUELLER.

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