THE COLLIERY GUARDIAN AND JOURNAL OF THE COAL AND IRON TRADES. Vol. CXI. FRIDAY, JANUARY 28, 1916. No. 2874. A Suction Gas Producer Using Bituminous Coal.* By R. V. FARNHAM. Anthracite is the favourite coal for both “ suction ” and “ pressure ” producers up to powers of 500 b.h.p., on account of the very low ash content, its non-caking qualities, and the very low percentage of volatile hydro- carbons which it contains. . Coke is used’, to some extent, because it is much cheaper than anthracite, but it is much more troublesome to gasify, due . to its porous nature, which necessitates more constant poking. Its ash content is also generally very high, and as the fuel consumption per b.h.p. is about 10 to 15 per cent, higher than anthracite, much more trouble with regard to clinker is experienced. . Again, the calorific value of coke ranges from 10,000 to 11,500 British thermal units per lb., while, on the other hand, from 13,500 to 14,500 British thermal units per lb. is obtainable from anthracite. When we con- sider the various drawbacks met with by the use of coke, anthracite is the fuel which users of suction pro- ducers rely upon, notwithstanding its high price to-day (35s. per ton, 1916). If we compare the composition of anthracite and the ordinary bituminous coal, some idea can be formed of the difficulties to be met with in adapting a suction producer to gasify coal , of a highly bituminous nature. The following analyses are typical examples of the two classes of coal :— Table I.—Anthracite. Percent., Fixed carbon .................'. 85’2 Volatile hydrocarbons.......... 9*4 Sulphur........................ 0*8 Moisture................... 2*1 Ash ....................... 2’5 100’0 Table II.—Bituminous Coal. Per c. Per c. Volatile matter, gas, tar;etc... 33*22 Sulphur..................... 0*59 ---- 33*81 Fixed carbon ............ 60*05 Sulphur................... 1*09 Moisture ................... 7*65 The suction - producer illustrated in fig. 1 has been designed for making gas producers more adaptable to the fuels which are more easily obtained and considerably , cheaper than anthracite. It shows a 100 b.h.p. producer in section, and was the original design which was tested •as far back as 1910 by Dr. Dugald Clerk. A is the space into which the coal is fed through the door at that level, B is the chamber which contains the initial charge of gas coke, F F are the steel rams coupled to the rising grate. These rams have machine- cut teeth, which gear into the pinions which are .clearly shown. C is the main steam raiser. E the sliding plate for supporting the.fuel bed whilst charging the producer with coal. A 3-b.h.p. electric motor is suitably coupled to the gearing which operates the sliding plate and the rising and falling grate. Suitable reducing gear is con- nected to the clutch gearing, which, in turn, carries out the four operations, viz.:—(1) The . raising and lowering of the grate; (2) the inward and outward travel of the sliding plate. , , This producer, during the aforesaid tests, developed 4,824 b.h.p. hours in 48 hours. The grate area is 706-8 »sq. in., equal to 6’6 sq. in. per b.h.p. A small cooler was fitted between the engine and the producer to cool the gas to atmospheric temperature, and wins the only chamber employed in rendering, the gas fit for use in the engine. Bituminous coal is used containing 34 per cent, gas and tarry matter, and after the run no trace of tarry matter was found on the' valves of .the engine. The essential features of the producer are the rising * From a paper read before the Institution of Engineers. z and Shipbuilders in Scotland. and falling grate (fig. 2) and the sliding plate, and the chief characteristic is the feeding of the coal through the. firing door at the bottom of the producer. The method of working'the producer is as follows :— Ordinary gas coke is fed on to the grate when this is at its lowest position through the hinged door at the top of the producer. This charge of coke is.brought up to the level of the gas outlet. The engine is allowed to, run from one to two hours, according to the load, with gas which is generated from this coke only. As soon Fig. I—Sectional Elevation of Producer. as it is necessary to begin to charge the producer with bituminous coal, the grate is raised to the level of the sliding plate, the travel of which is about .10 in. The sliding plate is'now driven across the fire between the bottom of the fuel bed and the top surface of the grate. The grate is now lowered’to its lowest position, and the bituminous coal is then thrown through the firing door opening on to the grate. As soon as this space is packed tightly with the coal, the sliding plate is withdrawn, allowing the incandescent fuel to gradually settle on to the. fresh fuel. The firing door is now closed, and the same procedure is followed at intervals, which are determined by the load that the producer is carrying. Several disadvantages would appear to arise during the period of charging, as it is well known by gas pro- ducer designers how important it is to exclude air whilst charging an ordinary suction producer gasifying anthracite or gas eoke in the orthodox way. These dis- advantages, however, do not appear in practice, since the pressure of the rising grate causes the fuel,to become very dense and compact, preventing channels or cavities in the fuel column, and obviating the necessity for poking. This characteristic of applying pressure to the glowing mass of incandescent carbon is very important. It will be realised that the pores of fhe fuel bed are closed by this pressure, the oxygen of the air entering the firing door, whilst chargings comes into contact with a body of fuel which is of very close formation, and the neces- sary reactions take place, with the result that the gas generated is-the same approximately. as was generated immediately before charging. Should this pressure be non-existent, a large percentage of carbon dioxide (CO2) and free oxygen .would be present in the gas generated. The calorific5 value would also be so lowered' that the engine would probably develop less’power, or probably •stop altogether.: ' . ' ' Secondly, if air and steam are being drawn through the outside steam raiser, C (fig. 1) to the underside of •, the grate immediately before charging, and the percen- tage of hydrogen (H2) is from 12 to 20 per cent., and the calorific value is from 130 to 140 British thermal units per cu. ft. of the gas generated, then a similar quantity of hydrogen (H2) must be present an the gas, ■ which is being generated, while the firing door is wide open. This hydrogen content is obtained1 whilst the operation of charging is going on by the simple opera- tion of damping the coal with water before it is intro- duced into the producer. Thirdly, after the firing door is closed and the sliding platex withdrawn, it is most important to bring the fresh charge of fuel to a temperature that will prevent the regular supply of steam from condensing as quickly as possible, because the first object the steam comes into contact with, on entering the space under the grate, is cold and wet coal. This would, naturally, condense the steam flow, and the result would be that the gas would be minus its hydrogen (H2) content. Careful observations have been made' to ascertain how soon .the wet coal ceases to generate steam, .and how soon this wet coal reaches a temperature above 212 degs. Fahr., and the results that have been obtained show that the process is practically automatic. The raising of the fresh charge of coal to the requisite temperature, or rather a temperature that will prevent condensation, is carried out by the simple arrangement of pre-heating the air by means of an iron casing bolted to the top cover of the producer. The air entering the casing on one side of the cover is distributed over the entire sur- face of the producer top cover, and discharges through a pipe bolted to the outside steam raiser.. The tempera- ture of the air is as high as 350 degs. Fahr, when it first comes into contact with the water flowing round the rings of the steam raiser itself, and, , consequently, enters the space under the.grate slightly lower than this. , While minor mechanical and gasification difficulties were being constantly met with and finally overcome in the 100 b.h.p. size, it was not until the larger sizes Fig. 2.—Plan of Rising and Falling Grate. were made that very real difficulties began to assert themselves. The small size had a grate area of only 4-9 sq.ft., or 2 ft. 6 in. diameter, and the length and width of . the sliding. plate being only ■ some 5 ft. by 2 ft. 10 in., no trouble was met with in employing an ordinary steel plate of a thickness of f in. When this plate was withdrawn after charging, the front end of the plate was found invariably to be red hot, and as the plate was bolted to the right- and left-handed screw nuts in a very rigid manner to the back end of the plate, this naturally caused severe buckling to. take place. The method employed in driving the plate across the .fire was, however, sufficiently strong to partially straighten the'plate during the next charging operation.' It was not until the. diameter of the grate was increased to 3 ft. 94 in. (250 b.h.p.) and 5 ft. 10J in.