US3367309A - High-pressure dry steam system and method of controlling the same - Google Patents

Description

Feb. 6, 1968 E. L. PLAGMAN, JR HIGH-PRESSURE DRY STEAM SYSTEM AND METHOD OF CONTROLLING THE SAME Filed May 10, 1966 9Jl l Unite This invention relates to a high-pressure dry steam system and to a method of controlling the discharge of condensate for the system so that the rate of condensation and discharge thereof from the system are maintained in balance with the high pressure dry steam output of the steam generator.

This invention relates particularly to a high pressure dry steam system employing a steam generator having a predetermined rated output of combined pressure and dry steam and connected to a plurality of high pressure dry steam consuming devices having a total actual capacity which does not exceed the rated capacity of the generator. The generator may comprise one or more separate units connected to a common header or to a main steam line.

More specifically, the invention relates to the method and means for restricting the rate of discharge of accumulated condensate from each device after a down period so that the rate of discharge of the total condensate, including both that accumulated and that currently being produced, in the entire system is maintained within limits such that condensate formation does not exceed the output capacity of the steam generator, thereby preventing carryover of wet steam and water from the generator into the system, and so that, after the system is brought up to operating pressure and temperature each device is maintained at its rated capacity.

Though the present invention is directed particularly to the high pressure dry steam systems, it also results in some benefits when used on the lower pressure systems.

For purposes of illustration, the invention is disclosed as applied to modern steam laundries, its use for other purposes being readily apparent from the illustrative example. Modern steam laundries generally employ the high pressure steam generator which may consist of one or more generating units connected to a common header from which extends a main steam line connected by branch lines to various types of equipment, such, for example, as tumblers, driers, steam boards, presses, ironers, shell and tube heaters, and the like.

The generator usually has a rated capacity of a predetermined number of pounds of water per hour evaporated into steam at predetermined temperature and pressure. This capacity sometimes is listed as generator horse power or B.t.u. capacity, and can be converted readily to the number of pounds of water converted to steam at the requisite temperature and pressure.

Originally, in such systems, the practice was to connect a common steam trap to the outlets of the various devices for discharging condensate therefrom. This practice was unsatisfactory and was superseded by the practice of utilizing separate steam traps, one on each of the steam devices, and usually one for the header and one for the main steam line. In the case of multiple roll ironers, each roll was considered to be a separate device, and a separate steam trap was provided for each.

Steam traps are well known and are designed to permit condensate to escape continuously or to accumulate and escape intermittently. Some operate in response to condensate level and some in response to temperature changes. Others operate electrically. The specific type used was unimportant, but whatever type was selected, it was such that, when open, it discharged condensate very States Patent rapidly. This was because, since the system was not in balance, as hereinbefore described, a certain amount of wet steam from the generator resulted, and the steam trap selected was one of a sufii-ciently large output to handle not only the normal condensation from the steam devices, but also the carryover. A safety factor was allowed which might vary from one to ten times the normal condensation rate of the device. It was believed that high efficiency was obtainable only if the condensate from each device were discharged as rapidly as possible. Thus the selected trap for a given device was adequate to discharge condensate therefrom at a much higher rate than the rated capacity of the device.

When these prior systems have been shut down for a period, as in closing down overnight, the steam generator, the header, the main steam line, and the steam heated devices all cool to an appreciable degree below operating temperature. Consequently, a large accumulation of condensate in the system results and a large amount of metal must be brought up to temperature in restoring the system to operation. When heating of a system in such a condition is initiated, condensate is produced at a higher rate than in the final operating range. The pressure in the system is far below normal. Consequently, the condensate reaches the steam traps and is discharged into the return line. The steam traps have a capacity of from one to ten times the normal condensate require ments of the steam devices, because the trap capacities are so great and the traps are fully open when the pressure starts to rise. Therefore, the steam being generated begins to flow more rapidly through the pipe lines to the devices, and then through the steam traps, which are still open because of condensate and lack of line pressure to close them. In the initial warm-up stages, as the pressure increases the velocity of condensate flow at the discharge side of the steam traps and becomes greater than the output of the generator. As a result of this velocity increase, the steam being generated and fed into the steam line is not sufficiently heated, and steam in a wet condition issues from the generator and flows throughout the pipe lines and steam devices. This starts a cycle in which the traps discharge both the normal condensation of the devices plus the carryover of wet steam. In so doing, they cause this cycle to continue.

According to the system of the present invention, the discharge of the traps is limited so that they cannot dis charge at a greater rate than the generator is capable of producing. Thus, in the present system, the generator is not called upon at any time to produce more than its rated or actual capacity.

Thus, While the generator is being brought up to operating temperature, it is subjected to an excessive and accumulative burden; first, the large accumulated amount of cold condensate being fed into the generator retards high temperature dry steam generation; second, the large amount of cold piping and number of cold devices being heated up concurrently causing exceedingly rapid temperature reduction of such steam is fed to the line and the formation of more condensate; third, the loss of heat from the generated steam to the wet steam and moisture in the system aggravates the situation; fourth, with traps open widely, the pressure in the system does not build up rapidly and the fiow of steam from the generator begins before such steam is at the temperature and pressure required; and fifth, the reduced pressure increases the introduction of wet steam from the generator.

Thus, steam from the generator enters the system while the steam is wet and before it is at the requisite temperature and pressure, often carrying over into the system a large amount of suspended droplets of water.

The carryover of water, whether as free droplets or as wet steam, lowers the generator level to such a degree that make-up water must be fed into the generator to bring the water level up to that required. This again chills the generator and aggravates the condition. This make-up water is a loss in that, should the system become fully operative, too much water is present. Such excess eventually must be disposed of or separately handled.

As a result of these concurrently existing and cumulafive effects, if the operator is not extremely careful in manually controlling each steam device as it is being cut-in to the system so that the generator can maintain a lead in the rate of generation of high pressure dry steam over the rate of condensate formation, the generator can catch up only after a long period of inoperativeness of the system.

The carryover of water from the steam generator into the system has long been a problem for which a solution was lacking.

The attempted solution for rectifying such conditions was to see that the steam traps had capacities in excess of the rated capacity of the devices with which they were used, so that the condensate could flow from the steam side of the system as rapidly as possible.

This attempted solution overlooked completely that this problem resulted from incapacity of the generator to gain on the capacities of the traps. It aggravated the very problem it was meant to solve.

In accordance with the present invention, it has been found that all of the devices under such conditions can be connected into the main line in relatively rapid succession, or concurrently, if the rate of discharge of the condensate from the various devices is limited so that the total rate of discharge from the system does not exceed the rated capacity of the generator. Thus, by having proper flow control orifices on the devices, the rate of discharge of condensate from each device is reduced sufiiciently so that the steam from the generator enters the equipment more slowly, following up on the very slow regression of the relatively cool accumulated condensate from the system.

This causes the pressure in the main steam line to increase more rapidly to the temperature and pressure rating of the generator, thereby reducing or preventing carryover of water from the generator. As a result the output of dry high pressure steam by the generator ever comes the formation of condensate, forcing it gradually out of the lines and devices and building up the temperature of all the devices at a rate consistent with the generator capacity. The rate of escape of condensate from each device is independently controllable so that no one device is freely vented to the return line. Hence no device can initiate water carryover from the generator.

Specific objects and advantages of the invention will become apparent from the following description wherein reference is made to the drawings, in which:

FIG. 1 is a diagrammatic illustration of the high pressure dry steam system employing the principles of the present invention;

FIG. 2 is a diagrammatic illustration of one of the steam operated devices thereof in the form of a bank of individually controlled units.

Referring to FIG. 1 of the drawings, the system, as embodied in a steam laundry, comprises a high pressure, steam generator 1 connected to a suitable header 2 from which leads a main steam line 3. A condensate return line 4 is provided returning condensate to the steam generator 1. The return condensate is delivered by the line 4 to condensate receiving and return equipment 5 which forces it back into the generator. Likewise, a motor driven pump 6 is provided for pumping, from a suitable external source, make up water into a receiver or injector for the generator.

The specific steam operated devices used in the system may be varied depending upon the purposes of the particular installation. For purposes of illustration, a closed system is shown and includes such devices as a shell and tube heater 10, an ironer 11, a tumbler 12, a steam board 13, and a presser 14. The closed steam system is preferred so as to conserve the condensate for re-use. However, if desired, an open system can be used, the steam traps thereof discharging the condensate to an open sump or drain. The connections and fittings for the devices are the same.

Referring particularly to the heater 10, it is connected by a branch line to the main line 3, a suitable stop cock 16 being interposed between the main line 3 and heater 10. The heater 10 has an outlet which is connected by a discharge line 17 to the inlet of a steam trap 18 of one of the conventional types. Usually the traps selected are of the type which open and discharge condensate when a predetermined condensate level is reached therein. Other types, such as those which operate on the basis of the temperature or weight of the condensate may be used.

A suitable stop cock 19 is provided between the line 17 and the inlet of the trap 18. A stop cock 20 is provided between the outlet of the trap 18 and a branch return line 21. A by-pass line 22, including a stop cock 23, is provided in by-passing relation to the stop cocks 19 and 20. The various cocks are arranged for proper servicing of the equipment;

customarily when separate traps are employed, one for each steam device, each trap selected is such that when open to discharge condensate it has a capacity for discharging the condensate at a rate much greater than than required by its associated device.

In accordance with the present invention, the trap 18 is provided with a flow control orifice means which reduces the rate of fiow of condensate from the trap so that, while the trap is open, the condensate escapes gradually from its associated device. As hereinbefore mentioned, it is necessary to reduce the rate of flow so that the total of discharge from all of the devices in the system does not exceed the horse power or rated capacity of the generator.

While it is possible to incorporate in the body of the trap a flow control orifice means of proper size to reduce the rate of flow to that required, it is to be noted that usually the discharge orifices of the traps even though adequate to discharge at a rapid rate and much larger than can be tolerated in the present sytsem', are nonetheless small. If of a size for the limiting of the flow as herein contemplated, they would be so small that would clog easily. Also, if within the trap, they would be diflicult to service.

Accordingly, orifice means 24 are provided in the discharge line 21 between the outlet of the trap 18 and the return line 4.

This orifice means preferably is in the form of a manually adjustable needle valve of which the elfective orifice size can be adjusted with precision to assure a maximum rate of fiow considerably below that of the trap 18 and a minimum rate of flow adequate to assure discharge of the condensate from the trap when the associated device is functioning at its rated capacity. Such an adjustable orifice is preferred as many factors enter into the formation of condensate and may vary with the seasons of the year, and compensating adjustment may be required from time to time. If this system is not subjected to these changing extraneous conditions, then a fixed orifice, preselected in accordance with the requirements of the systern, may be employed.

Generally, between the orifice 24 and the return line 4, a check valve 25, opening to permit flow of condensate to the return line and closing to prevent the return flow therefrom, is provided.

Furthermore, for purposes of isolating diiferent parts of the equipment for service and repair, a stop cock 26 is provided between the check valve 25 and the return line 4.

Since the installation and fitting for each device is essentially the same except for the size of the orifice means, check valve, and stop cocks, the specific installation of each device will not be described in detail, except to note that generally they are connected in parallel across the steam line and the return line.

The ironer 11 employs a steam trap 30 and an adjustable orifice 31, the tumbler 12, a steam trap 32 and an adjustable orifice 33, the steam board 13, a trap 34 and an adjustable orifice 35, and the press 14, a steam trap 36 and an adjustable orifice 37.

At this point it is to be noted that the main steam line and the header are also operating devices, inasmuch as a certain amount of steam is consumed by them in transmitting it to the other steam consuming devices and condensate is produced accordingly. The branch lines leading to the recited steam operated devices are usually short and the condensate therein is considered to be part of the condensate of that specific device. Thus, in addition to the devices heretofore recited, the header 2 is provided with a trap 40 and an adjustable orifice 41. The main steam line 3 is provided with a trap 42 and an adjustable orifice 43. These traps and orifices likewise have the usual stop cocks and check valves, arranged as described specifically as those used in connection with heater 10.

As illustrated in FIG. 2, the ironer 11 may comprise a plurality of individual units or rolls 110, each of which has its individual trap 30a with an adjustable orifice 31a, and check valve and isolating stop cocks. In such case, the operating efiect is the same except that more accurate control can be obtained, each roll becoming a separate steam consuming device. If desired, however, one trap may be used for the ironer 11.

Thus, in operation the rated capacity of the generator and of each of the various devices being known, traps are chosen as hereinbcfore described for the devices, respectively, including one for the main steam line 3 and one for the header 2.

Having installed the orifices, and with the system cold, the generator is started. Each orifice remains fully open to determine whether the steam generator has the capacity to purge the system of condensate and bring it up to the operating temperature and pressure. Generally, it cannot do so. Each orifice may be reduced in size by operation of the needle until it becomes apparent that the steam generator can catch up within a reasonable time with the formation and discharge of condensate. Watching the gauge of the steam generator and knowing its rated capacity, one can determine its rate of approach to its rated temperature and pressure output. If losing, each of the orifices is reduced still further until a balance is obtained. If, under such conditions, any device is not being kept purged of condensate, the orifice therefor can be increased slightly, and one or more of the other orifices increased if necessary. Necessarily, since the devices, including the steam line and header, do not exceed the rated capacity of the generator, a balance is soon reached. Further refinement for optimum efiiciency can be obtained by reducing each orifice still further so that each has as slow a flow rate as is consistent with the rated capacity of its associated equipment. Once the desired balance is obtained, the needle valves may be locked in the final adjusted position to assure that they will not inadvertently be thrown out of balance in the future.

With this arrangement, the steam generator can readily bring the system up to the pressure and temperature which is required in the equipment, and thereafter maintain said pressure and temperature. The main line, header, and the devices are gradually purged without at any time over-taxing the generator so that the carryover of water from the generator is eliminated.

Should it happen that the total of rated capacities of the steam devices exceeds the capacity of the steam generator, then additional steam generating capacity must be added so that the total generator capacity exceeds the total rated capacities of the devices in order for the present invention to be fully effective.

Having thus described my invention, I claim:

1. In a steam system:

a steam generator having an output within a predetermined range of combined pressure and steam temperature;

a plurality of steam consuming devices connected thereto for receiving steam therefrom and having a total rated capacity not exceeding the rated capacity of the generator;

each of said devices having an outlet;

steam trap means connected to the outlets, respectively, each trap means being capable of discharging all of the condensate of the steam utilized by its associated device while preventing the escape of steam from its associated device;

characterized in that each of said trap means includes flow limiting means permitting discharge of condensate up to, but not substantially exceeding, the rated capacity of the associated device when the trap means are fully open; and

said tlow limiting means of all of the trap means in the system are related to the generator so that their combined effect is to restrict the rate of discharge of condensate from the entire system to a rate such that the system remains within the output capacity of the generator and thereby prevents carryover of wet steam and water from the generator into the system.

2. The structure of claim 1 wherein the fiow limiting means of each device has a condensate flow rate capacity substantially equal to the rated capacity of the associated device.

3. The structure according to claim 1 wherein said trap means are such that, in the absence of their associated flow limiting means, they would have a combined maximum discharge rate greater than the generator capacity.

4 The structure according to claim 1 wherein adjustment means are provided for the flow limiting means, respectively, and are operable to adjust the effective rate of discharge of condensate through their associated flow limiting means independently of each other.

5. The structure according to claim 1 wherein the fiow limiting means for each trap means is an adjustable needle valve having its inlet connected to the outlet of its associated trap means.

6. The structure according to claim 1 wherein a condensate return line is provided, discharge lines connect the trap means, respectively, to the condensate return line, condensate receiving and return equipment is connected to the return line and to the steam generator and is operable to return the condensate to the generator; and

each of said flow limiting means is connected in the discharge line of its associated trap means between the outlet of the associated trap means and the return line.

7. The structure according to claim 6 wherein manually individually adjustable needle valves are provided for the trap means, respectively, each needle valve is disposed in the discharge line of its associated trap means, and the flow limiting means of the associated trap means is the orifice of the associated needle valve.

8. The method of increasing the efiiciency of a steam system which includes a steam generator having an output within a predetermined range of combined pressure and steam temperature, and a plurality of steam operated devices connected thereto for receiving steam therefrom, each of said devices having an outlet;

said method comprising discharging the condensate of the steam utilized by each device while preventing the escape of steam therefrom, and controlling the 7 8 rate of discharge of said condensate from each de- References Cited 3 1 i ifi fiif i iffio i i "i 3322 UNITED STATES PATENTS ensae rorn e n e y ra e suc 1701 143 2/1929 Clarke 122-4 h h t t th the system rernams w1t 1n t e on pu range of 6 3,076,445 2/1963 Ohlhaver 122 459 generator and thereby prevents carryover of wet 5 steam and water from the generator into the system. CHARLES J. MYHRE, Primary Examiner.

Claims (1)

1. IN A STEAM SYSTEM: A STEAM GENERATOR HAVING AN OUTPUT WITHIN A PREDETERMINED RANGE OF COMBINED PRESSURE AND STEAM TEMPERATURE; A PLURALITY OF STEAM CONSUMING DEVICES CONNECTED THERETO FOR RECEIVING STEAM THEREFROM AND HAVING A TOTAL RATED CAPACITY NOT EXCEEDING THE RATED CAPACITY OF THE GENERATOR; EACH OF SAID DEVICES HAVING AN OUTLET; STEAM TRAP MEANS CONNECTED TO THE OUTLETS, RESPECTIVELY, EACH TRAP MEANS BEING CAPABLE OF DISCHARGING ALL OF THE CONDENSATE OF THE STEAM UTILIZED BY ITS ASSOCIATED DEVICE WHILE PREVENTING THE ESCAPE OF STEAM FROM ITS ASSOCIATED DEVICE; CHARACTERIZED IN THAT EACH OF SAID TRAP MEANS INCLUDES FLOW LIMITIG MEANS PERMITTING DISCHARGE OF CONDENSATE UP TO, BUT NOT SUBSTANTIALLY EXCEEDING, THE RATED CAPACITY OF THE ASSOCIATED DEVICE WHEN THE TRAP MEANS ARE FULLY OPEN; AND SAID FLOW LIMITING MEANS OF ALL OF THE TRAP MEANS IN THE SYSTEM ARE RELATED TO THE GENERATOR SO THAT THEIR COMBINED EFFECT IS TO RESTRICT THE RATE OF DISCHARGE OF CONDENSATE FROM THE ENTIRE SYSTEM TO A RATE SUCH THAT THE SYSTEM REMAINS WITHIN THE OUTPUT CAPACITY OF THE GENERATOR AND THEREBY PREVENTS CARRYOVER OF WET STEAM AND WATER FROM THE GENERATOR INTO THE SYSTEM.

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