A practical treatise setting forth the principles of gas-engines and producer design, the selection and installation of an engine, conditions of perfect operation, producer gas engines and their possibilities, the care of gas engines and producer gas plants, with a chapter on volatile hydrocarbon an…
Gas Engines and Producer Gas Plants Alternative Fuels POWER GAS PRODUCERS Alternative Fuels Everything you've ever wanted to know about making and passing gas... Pressure and Suction Types 1. It is sometimes desirable or necessary to operate a gas engine independently of a central gas plant. In such cases, it is possible to produce the fuel gas required to run the gas engine at a lower cost than when using either illuminating gas or the more volatile grades of liquid fuel, such as gasoline and distillate of petroleum. This has led to the gradual development of an apparatus known as a power-gas producer, which is practically a small gas plant located near the engine, to which it furnishes gas. The process of making gas from coal, coke, or charcoal by means of such a producer is a simple one. The gas-generating and purifying devices are of such size as to be readily installed in power plants using gas engines and operating under ordinary conditions. They occupy but a small amount of space, and the attendance, even in a fairly large plant, requires only a portion of the time of one man. 2. Classification of Producers: Modern gas producers may be divided into two general classes namely, pressure producers and suction producers. In pressure producers, the gas is generated by forcing a blast of steam from a boiler, or of moistened air from a blower, through a bed of incandescent fuel. The gas is purified in a scrubber, stored in a gas holder of suitable capacity, and supplied to the engine at a pressure of from 2 to 3 ounces. Pressure producers are generally used in large power plants and where more than one engine is supplied from the producer. They are also adapted to the use of different kinds of fuel. In suction producers, air and water vapor at atmospheric pressure are drawn through the incandescent fuel by the inhaling or suction action of the engine, due to the partial vacuum produced in the engine cylinder during the suction stroke of the piston. The gas so generated is cooled and purified in the same manner as in the pressure producer. The volume of gas in a suction producer is thus never in excess of that required by the engine, and consequently it is not necessary to provide a holder, the gas being drawn directly from the producer to the engine cylinder. The amount of gas generated depends on the force of the suction or the number of inhalations transmitted from the engine cylinder to the producer. The engine governor controls either the volume of the charges or the number of charges required to operate the engine under any load. 3. Power Gas.-The pressure process of manufacturing producer gas for power purposes has not been materially changed since its introduction 20 years ago (1887) by Dowson, in England. Producer gas had previously been used for heating purposes, in which case it was desirable to keep the temperature of the gas as high as possible before being burned. In generating power gas the conditions and requirements are materially different, the desired object being the transformation of the heat in the coal into the chemical energy of cold gas, because it is only in a thoroughly cooled condition that gas can be used efficiently in engines. In the pressure process of generating gas for heating purposes, the dry air is heated before being introduced into the producer; in the generation of power gas, on the other hand, the object is to reduce the temperature of the gas as much as possible by admitting to the producer a certain amount of air and water vapor, so that, when the mixture is brought in contact with the burning fuel, hydrogen will be liberated. With even this cooling effect, however, the gases leave the producer at a temperature that is generally above 900 degrees F. The process of manufacturing power gas consists principally in heating some form of fuel to a very high temperature in a vessel from which the atmosphere can be excluded. The vessel in which the heating takes place is called the producer, or generator. The vessel in which water is heated, in order to supply moisture to the air that is admitted to the producer, is called the evaporator, or boiler. After the gas is made in the producer, it is purified and used directly, or else stored in suitable tanks. The several steps in the process of gas generation will be treated in detail in connection with the various types of producers. PRESSURE GAS PRODUCERS 4. One of the first types of pressure producers, as introduced by Dowson in England, and of which several plants have been installed in America, is illustrated in Fig. 1. The boiler a generates steam at from 60 to 75 pounds pressure, the steam being conveyed to the injector b through the pipe c. In the injector, the steam is discharged through a small nozzle, and the issuing current draws with it a certain amount of air from the casing d surrounding the pipe e, through which the hot gases leave the producer f. Thus the injector serves merely to deliver a mingled stream of air and steam to the ash-pit g of the producer, beneath the grate. The producer consists of a cylindrical shell made of steel plates and lined with a highly refractory grade of firebrick. A hopper h, which is closed toward the atmosphere by a removable lid i, and against the interior of the producer by means of the bell j, conducts f uel to the producer while in operation. The bell being tight against its seat, the lid can be removed and the hopper filled with fuel. After closing the hopper, the bell is allowed to drop, permitting the fuel to enter the firepot of the producer, where it descends to the grate and is consumed, the ashes and clinkers being removed through the door k. 5. The steam entering the producer is decomposed into oxygen and hydrogen while passing through the incandescent fuel. This oxygen, together with that which is in the air mixed with the steam, unites with the carbon of the fuel to form carbon dioxide and carbon monoxide. These gases mix with those produced from the fuel by the heat and pass upwards through the port I and the pipe e. The pipe e is provided with fittings having removable handhole covers, for the purpose of giving easy access in case it becomes necessary to clean the pipe. The gas is next forced through the water box m, where it is washed and most of the impurities removed; it then enters the scrubber n, which is filled with coke to within a few inches of the outlet pipe o near the top. As the gas rises in the scrubber, it is met by a descending shower of water distributed over the entire area by means of the sprinkler p. The water cools the gas and carries away some of the impurities, leaving a small portion deposited on the coke. The coke is placed in the scrubber with the larger pieces at the bottom, the sizes gradually diminishing toward the top, and need not be renewed for a period of from I to 2 years, according to the quality of the fuel used in the producer and the amount of tarry matter contained in the fuel. After the coke becomes clogged, the scrubber is emptied and fresh coke provided. Any dust or other impurities that the gas may contain after leaving the scrubber is removed while passing through the purifier box q - sometimes called a sawdust purifier which consists of a square box with a removable top and contains a series of wooden gratings r, over which are spread layers of sawdust or similar material. The gas is now ready to be stored in a holder, not shown in the illustration, from, which it is supplied to the engine in the same way as illuminating gas, but of course in larger quantity, proportionate to its lower heating or calorific power. 6. The gas generated when the producer is first started is of very poor quality and unfit to be stored in the holder. It is therefore permitted to escape into the atmosphere through the smoke and waste-gas pipe s, until, by a test made at the tube t, the gas shows that it is of the proper quality, by burning with a bright blue flame. As soon as the quality has come up to the desired standard, the valve u in the waste pipe is closed, and the gas is allowed to pass on its way through the scrubber to the holder. The overflow from the water box m passes through the water seal v, which permits the water to flow to the sewer without allowing any gas to escape. It will be seen, by an examination of Fig. 1, that all pipes between the producer and the holder are provided with fittings having handholes and covers, so that the pipes can easily be cleaned as occasion may require. It must be understood that, especially when using the poorer grades of coal, some of the impurities contained in the gas will adhere to the walls of the pipes, and in time sufficient quantities may ,accumulate to interfere with the free flow of the gas from the producer to the engine. The pressure of the gas at the point where the injector b connects to the ash-pit of the producer is about 8 inches of water. This pressure gradually diminishes on account of the resistance that the gas encounters during its passage from the producer to the holder, Measured by a water gauge, the pressure in the pipe e between the producer and the water box is equal to about 6 inches; after leaving the, scrubber, the pressure is 4 inches, and before entering the holder it is 2 inches. SUCTION GAS PRODUCERS 7. Comparison of Suction and Pressure Producers. A comparison of the pressure producer with the suction producer discloses the fact that the chemical changes brought about In both types are practically the same. The difference between the two types is therefore. not in the nature of the product, but in the manner in which the gas is transmitted from the gas apparatus to the engine. The processes of generating and purifying the gas are the same in both cases; but in the pressure producer a pressure above that of the atmosphere is maintained by a forced draft, either from a low- pressure steam boiler or from a blower; while in the suction producer the pressure in any part of the apparatus or its connections is never higher than that of the atmosphere. The draft in the suction producer is furnished. by the engine piston during the suction stroke while the inlet valves are open, and the vacuum created in the cylinder causes the gas from all parts of the producer apparatus to flow toward the engine. The difference in pressure between the two systems is practically 8 inches of water; so that, in the suction producer, the pressure of the gas as it leaves the scrubber is about 6 inches of water below atmospheric pressure instead of 2 inches above, as in the case of the pressure producer. The relative difference in pressure in the various parts of the apparatus is the same in both systems, and the order of the operations of the process is necessarily alike in both cases. The suction type of producer does not require a large gas holder, a small cast-iron or sheet-metal tank being used instead. This tank is but slightly larger than the customary gas bag or pressure regulator used in connection with engines using illuminating gas. 8. Supply of Air and Moisture.-A suction gas producer of small capacity, in which the evaporator for supplying the necessary moisture to the air is mounted directly above the producer shell, is shown in Fig. 2. The apparatus consists of the producer a with a cast-iron shell; the hand operated blower b, for reviving the fire after a shut-down over night; the evaporator c; the hopper d; the water trap e; the water-seal box f; the scrubber g; and the gas tank or reservoir h. At each suction stroke of the engine, air is drawn into the top of the evaporator c, through the elbow i, which is open to the atmosphere. The evaporator is filled with water from a branch pipe taken from the main supply pipe and kept at a constant level by* an overflow pipe, not shown in the illustration, that carries any surplus supply to the, ash-pit j. The water in the evaporator is heated to about 170' F. by radiation from the burning fuel and by the hot gases that leave the producer through the port k. The air passing over the surface of the hot water absorbs a quantity of vapor, the amount depending on the temperature of the water; so that the quantity of the water vapor admitted with the air through the pipe I to the space below the grate is greater when the fire is hot than when it is low. The fire is hottest, of course; when the engine is carrying a heavy load. Under heavy load, not only does the increase in the amount of vapor enrich the quality of the gas generated, but also the moistened air has a correspondingly greater cooling effect on the grate and tends to keep the fire at a proper degree of intensity. 9. After entering the ash-pit below the grate, the mixture of air and steam is drawn upwards through the hot bed of fuel, where the steam is decomposed into hydrogen and oxygen, and the formation of carbon monoxide takes place. After transferring a portion of its heat to the water in the evaporator, the gas leaves the producer through the port k, passes through the water trap e, and enters the scrubber at the bottom. The water trap has two pipe connections to the water-seal box f, the lower pipe being provided with a valve m. While the plant is in operation, this valve is open and the water that accumulates in the bottom of the scrubber flows through the lower connection to the seal box f and thence through an overflow funnel n to the sewer. When the plant is shut down, the valve m should be closed, thus causing the water in the trap e to rise well above the lower end of the partition wall o. This closes the gas connection between the producer and the engine. Any excess of water then flowing to the seal box passes through the upper pipe attached to the trap e and thence to the sewer. 10. Passage Of Gas Through Scrubber. While the gas is rising through the coarse coke in the scrubber g, it is met by a descending stream of cold water which is distributed evenly over the area of the scrubber by means of the sprinkler p attached to the top cover plate. In this manner, the gas, from which some of its impurities have been removed while passing through the trap e, is now cooled and washed sufficiently to be delivered to the gas tank h in such condition that it contains no tarry or dusty substances to interfere with the successful running of the engine. When semianthracite or similar fuels containing higher percentages of tarry matter than pure anthracite or charcoal are used, it is necessary to add a sawdust purifier similar to that used in connection with the pressure producer shown in Fig. 1. 11. Supplying the Fuel.-The fuel is supplied to the producer shown in Fig. 2 through the charging device mounted above the hopper d, which consists of the funnel q and a smooth hollow ball r that can be turned, on its ground seat by the hand lever s. The ball has an opening at the top, so that it may be filled with coal through the funnel, after which it is turned over by a quick movement of the hand lever, bringing the opening in the ball in communication with the coal space in the hopper d. As soon as the ball has thus been emptied of its contents, it is turned back and the operations of filling and emptying are repeated until the hopper is filled to the desired height. When not in use for filling the producer, the ball is held tightly on its seat with screws and hand nuts. The quick turning of the ball leaves but a small fraction of a second during which the hopper is open to the atmosphere, and practically no air is admitted to the producer at that point. 12. Removing Ashes and ClInkers.-The removal of clinkers that form in the fire space of the, producer is facilitated by poke holes, with which the hopper is provided, that permit the fire to be stirred from above with suitable poking rods. The clinkers descend to the grate and are removed through the two fire-doors t, t, on opposite sides of the cast iron shell of the producer, while the ashes accumulating in the pit below the grate are drawn out through the ashdoor u. 13. Starting the Producer.-The hand-operated blower b serves to supply the blast necessary to start up the fire after the plant has been shut down for any length of time, say over night. During such a temporary shut-down, the process of gas making is practically stopped, except for the small amount of gas generated by the natural draft caused by the flue pipe v being kept open to the atmosphere by opening the flue valve w. While reviving the fire, the valve w, as well as the valve x in the vent pipe y, is kept open until the gas escaping at the test tubes z, z (one of which is placed in the pipes between the producer and the scrubber, and the other near the inlet to the engine) is of such quality as to burn with a bright blue flame. As soon as this is the case, the valve w, and the valves in z and z are closed and the engine is started in the usual manner. To secure prompt starting, it is found advisable to keep the valve in the vent pipe y open to the atmosphere until a few explosions have taken place in the engine cylinder, and then close it. LARGE-CAPACITY PRODUCER 14. A suction producer of larger capacity than the one shown in Fig. 2 and equipped with a separate evaporator is shown in Fig. 3. Instead of the cast-iron body shown in Fig. 2 in connection with the smaller type, the producer a Consists of a shell built of steel plate and lined with fire brick; but the hopper d and the coal-feeding device r are made of cast iron, and are essentially of the same construction as in the smaller producer. Instead of a hand blower,a belt-driven pressure blower b furnishes the draft for starting. The essential difference between the larger and the smaller plant is that the evaporator for heating the water in the smaller plant forms a part of the generator, while in the large plant it is a separate piece of apparatus and is connected to the generator by pipes, In the case of the larger, the evaporator consists of a cylindrical casting c with a hood e having a vertical dividing wall in the center, so that the air entering through the pipe f will be forced over the surface of the hot water in the evaporator before it passes to the ash-pit of the producer through the pipe g. Between the evaporator cylinder c and the hood is clamped a plate h carrying a number of vertical tubes i that are kept full of water, the level of the water being kept constant by an overflow pipe j slightly above the upper surface of the plate h. The hot gases leave the producer through the pipe k, and pass downwards and then upwards in the evaporator, being guided by the vertical partition l, and finally pass on to the scrubber m. In this manner, the water in the tubes is kept at the desired temperature, so that the required amount of vapor is taken up by the air while passing through the hood e to the ash-pit of the producer. In order to be able to control the amount of moist and dry air used, a regulating plate n is provided in the air pipe, by means of which the air-supply pipe can be opened to any desired extent to the atmosphere in the producer room, thus admitting cool air that has not come in contact with the hot water. The three-way, valve o serves to shut off the air connection to the evaporator when the fire is being revived by the blast from the blower. As soon as the gas has become of good quality, the blower is stopped and the three-way valve set so as to admit air in the regular way through the pipe g. COMBINED PRODUCER AND EVAPORATOR 15. Another suction gas producer of somewhat different design is shown in Fig. 4. The producer itself consists of a cylindrical steel shell lined with firebrick and fitted with a shaking grate a operated by the hand lever b. The hopper c, through which fuel is supplied to the producer, is sealed by the charging device d, so that any fuel placed in it can be admitted to the hopper without permitting air to enter the producer. From the hopper, the fuel descends … truncated (43,157 more characters in archive)