US2316744A - Method of gas utilization - Google Patents

Description

April -1 3, 1943.

D. S. MELLETT ET AL.

METHOD OF GAS UTILIZATION Filed Sept. 4, 1941 2 sheets-sheet-l WARM H/GH GEA/f 193970)? 0l? COMPRESSOR Cap WATER WARM lV/l 75A (Cou: WA TE/a Gear/# 57 N Rao/N5 INVEN-rons BY l L; ATTORNEY April 13, 1943.

D. s. MELLETT ETAL 2,316,744

METHOD OF GAS UTILIZATION Filed Sept. 4, 1941 TORNEY Patented Apr. 13, 1943 MEIHOD F GAS UTILIZATION Dana S. Mellett, Dearborn, Mich., and Geoffrey W. Robbins, Ardmore, Pa., assignors to Socony- Vacuum Oil Company, Incorporated, New York, N. Y., a corporation of New York Application September 4, 1941, Serial No. 409,554

(CL Bft-175.5)

4 Claims.

This invention is directed to a method for producing refrigerated or cooled water for oil refinery uses, and more particularly to a method for such purposes utilizing the energy stored in gaseous petroleum fractions normally available in substantial quantities at petroleum reiineries.

Oil reneries do a very considerable amount of heat extraction. While by far the greater portion of the heat extraction deals With hea-t at relatively high temperature levels, where heat in outgoing process products can be given up to incoming process charges in heat exchanging equipment, there remains a relatively quite large amount of low temperature level heat extraction, and practically the Whole of this lovv level heat is extracted by cooling with water in heat exchange relationship. With even a moderately sized refinery, the amount of cooling water circulated is enormous. used must be cooled and recirculated. The usual methods of cooling are by cooling ponds, spray ponds, and water cooling towers. The disadvantages of these older processes are the limitation of cold water temperature, loss of water, and cost of operation. The water temperature Obviously the water so obtainable by these methods is limited by atmospheric conditions, i. e., by the temperature and humidity of the air. Further, in atmospheric towers, operation depends on wind velocity, 'in forced draft towers the power demand is appreciable, and in any of these methods the water loss may range from 5 to 25 per cent. For many renery operations, the establishment of temperature levels below the reach of Water so cooled is necessary, and evaporative water coolers are used, for these, the vlower the water temperature desired, the higher is the vacuum that must. be maintained. Consequently for very low temperatures, the cost of steam for vacuum jobs is high, and, of course, a high pressure steam supply must be available. It may be mentioned that the vacuum cooling system is also limited by the temperature of the water available for condensing. The higher the condensing water temperature, the higher will be the steam requirement for any desired cold water temperature. l

Of course, refrigeratve methods in which some material', such as ammonia or carbon dioxide is compressed, cooled, and evaporated in a closed system are available. These processes are expensive at best and the cost of operation mounts rapidly as the desired temperature level is lowered. Additionally these processes in the usual forms are handled as indirect heat exchange systems. Due to these characteristics, the use of such processes is uniformly restricted to specialized service jobs, such as Wax chilling and the like.

This invention has for its' major object the provision of cooling capacity of comparatively low cost, both from the installation and operation standpoints, of great flexibility, and particularly adaptable to renery operations with a minimum of diiiiculty. Another object is the provision of such a process utilizing energy stored in gaseous' petroleum products normally in existence in almost all refineries, which has never before been so used.

Any modern refinery has many sources of petroleum gases at elevated pressures, such as the dry gases from absorbers, stabilizers, debutanizers, depropanizers, and similar eiiluent gases from many forms of operations from which gases are withdrawn at pressures higher than atmospheric. The normal nal disposition of these gases is a use as fuel or an open flare, both at quite low pressures. The necessary reduction of the exit pressures to waste or fuel pressure levels represents a very considerable amount of energy which may be made available for cooling duties. So far as is known, this possibility has heretofore been completely overlooked.

How this energy may be effectively utilized for this and for other purposes will be readily understood by reference to the attached drawings. The four iigures of these drawings show, in diagram form, various aspects of the process of ecililing low temperature cooling uids herein set In Figure 1 there is shown a simple and preferred form of the process of energy utilization. In this diagram, warmhigh pressure gas, exhausted from renery processing, such as, for example, from a usual type of debutanizingor stabilization operation, on cracked gasoline, or the like, at a pressure of from about 35 to 400 pounds or so,.and a. temperature of from about to 120 is delivered through pipe 5, and is passed through expansion engine 6, wherein it is expanded, doing work against the engine, and being cooled in the process. Useful work may be recovered, if desired, from engine 6 by utilizing it to drive a generator, compressor or other device l. To properly control the engine, and to permit further controlled reduction of the pressure upon the gas, thegas'leaving the engine 6 through pipe 8 is passed through pressure reduction valve 9 where its pressure is reduced to atmospheric or to the relatively low pressure held on the usual low pressure fuel supply pipe. The gag is further cooled in this adiabatic expansion. The expanded cured with an open tower into which the warm l water is so sprayed as to assure good contactv with the gases. The gases, .after contact, depart through pipe I3.

'I'his process of producing cool water is considerably more capable than any now in usefor the correctionL of temperature of renery cooling waters, and may be used for the production of water of hitherto unusual low temperatures. For example, with the reductionof gas at 100 F.

and 35# per square inch gauge-pressure to nor- I mal fuel supply line pressure of near atmospheric levels, it is relatively easy to reduce water te near its freezing point. This is beyond the capability of cooling towers or vacuum-cooling systems, and the energy source -is one that has not heretofore been utilized in any way. And the low temperature waters can be used to great advantage in increasing the eiilciency of existing processes over what has been attainable heretofore. For example, this low Atemperature water can be used to great advantage in chilling lean oil for absorbers, and in condensers for debutanizers. stabilizers, and the like. It is a virtual necessity for the Production and recovery of low-boiling point materials, such as ethane and ethylene.

Figure 2 illustrates another application of the process. In this case the operation of the tower is the same as that described above. The method of chilling the gas, however, is similar` to that used in the production of liquid air. The high pressure gas is expanded through a valve or nozzle 9, cooling by the Joule-Thompsoneifect. A portion of the cold low pressure gas is passed by pipe I5 through a heat exchanger I4 against the entering high pressure gas cooling the latter while being warmed itself. The remainder of the cold gas passes into the tower and cools the' water by direct contact, as described. 'I'he temperature of the gas entering the tower is controlled by varying the quantity of gas released through the heat exchanger. This process will not produce as much refrigeration as those illustrated in Figures 1 and 3 since no work is taken out of the gas.

Nor is any power recovered. However, the installation cost for this process would be considerably less than for those previously described, and consequently, it might be preferred in some situations.

.'n cases when the initial pressure of the gas is so high that expansion in a single stage would produce temperatures low enough to bring about icing or gas hydrate formation. the process may be carried out in two o r more stages as indicated in Figure 3. In this figure, the functions of items l5, 6, 1, 8, 9, I0, II, I2, I3 are the same as in IFigure 1, except that the pressure reduction in these items is only partial, the gas in pipe I3 passing to another engine I8, attached to another energy user l1, through pipe Il, through flnal pressure reduction valve I3 and into tower 20 the warm water supply for which at v2l may be perature of said fluid.

that in one small renery equipped with a high pressure gas recovery system, there is available in the eilluent gases power equivalent to 730 theoreticaly horsepower. Assuming an overall eiliciency of 50%, this power is equivalent to 1840 tons of refrigeration, or 22,000,000 B. t. u. per hour.

A very eillcient utilization of the energy so available may be made by using the operation diagrammed in Figure 4, wherein the engine 6, corresponding to the expansion engine 6 of Figure l, driven by high pressure refinery gas from pipe 5, drives a compressor 1, as in Figure 1, which compressor 1 is utilized for the compression of a recycled refrigerant gas, conveniently propane or a mixture of light petroleum gases, such as reflnery gas. Thecompres'sed gas flowing through pipe 26 is liqueiled by cooling water in condensorexchanger 21, and is expanded through valve 28 to pass through contact tower 29 to cool water introduced thereto by 30 and withdrawn by 3|, the gas being returned to reuse by pipe 32. f

We claim:

1. A method for the utilization of high pressure refinery gases to produce cooled fluids for heat extraction uses in refinery processing comprising partially expanding said gases to reduce the temperature thereof, and passing the cooled gases in direct physical contact with cooling fluid of higher temperature than said cooled gases, and subsequently expanding said gases to near atmospheric pressure, and again passing said gases in direct physical contact with cooling fluid of higher ternperature than said gases as 'passed in contact y therewith.

2. A method for the utilization of high presl' expansion, in direct physical contact with a sec-- ond portion of fluid to be cooled oi 'higher -temperature than said refrigerant gas after its expansion.

y 3. A method for cooling fluids for heat extraction uses' comprising expanding high pressure refinery gases to reduce the temperature thereof, and passing the so-cooled gases in direct physical contact with a fluid of .higher temperature to reduce the temperature of said fluid.

4. A method for cooling fluids for heat extraction uses comprising expanding high pressure refinery gases and extracting work therefrom to reduce the temperature thereof, and passing the so-cooled gases in direct physical contact with a fluid of higher temperature to reduce the tem- DANA S. MELLETT. GEOFFREY ROBBINS.

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