"Regenerative Benches," by Mr. H. C. Slater, Milwaukee, Wis. "Wrinkle Department," edited by Mr. F. H. Shelton, Philadelphia, Pa. The President appointed the following committees : On Applications for Membership.-Thos. D. Miller, A. H. Barret and B. W. Perkins. On Auditing.-Jas. T. Lynn, Jno. Gimper, Geo. McLean. The Secretary-Treasurer submitted his annual report. JAS. W. DUNBAR, Secretary. REPORT OF SECRETARY-TREASURER. RECEIPTS. Cash on hand May 1, 1899.. Annual dues Membership fees 1899 Membership fees 1900 Sale of badges (15) .... Sales of Proceedings (22 Vol.) DISBURSEMENTS. Secretary's salary Postage Telegrams 600 copies Proceedings years 1896-'97-'98, including ex pressage, freight and postage. Passenger Associations Dues American Meteorological Society Educational Fund ... $1,220 17 1,246 85 460 00 40 00 52 50 44 00 $3,063 52 .$ 400 00 98 80 10 94 843 58 20 50 IO 00 100 00 900 copies papers read at Twenty-second Meeting.. Cuts, electrotypes, drawings, etc... 242 65 174 00 Executive Committee meeting Chicago, May 12, 1899.. The President introduced Mr. Howard C. Slater, of Milwaukee, Wis., who read the following paper on REGENERATIVE BENCHES. By the term "Regenerative Benches" I understand is meant those benches in which the air necessary for combustion, secondary or primary or both, is, before arriving at the place of combustion, heated in recuperators or regenerators by heat absorbed from the products of combustion, after they pass the last retort in their course and before entering the main flue or chimney. The advantage of preheating the secondary air is, I believe, acknowledged by all who are familiar with gaseous firing, whether this preheating be done by absorption of heat from the products of combustion or otherwise. The efficiency in the use of the heat given out by the combustion and transmitted through the walls of the retort is, other things being equal, greatest with the greatest difference of temperature between the inside and outside of the retort. Hence, that which increases the temperature of combustion, as the preheating of the air supply, tends to increase the efficiency of the apparatus. This preheating can be accomplished by absorbing heat from the products of combustion after they have given up as much as may be to the retort, where the heat is wanted, and still leave enough heat in these gases, as they pass into the chimney, to produce the necessary draft for the operation of the bench. The temperature of the outside of the retort being about 2,000° F., and a temperature of from 500° to 600° F. sufficient for draft, it is easily seen that a saving in the fuel account may be realized, if we can return into the setting this amount of heat, which would be given up by the products of combustion on cooling from the higher to the lower temperature. Whether this saving in fuel is counterbalanced by the extra cost for recuperators must be decided by local conditions. From a paper by Mr. G. Helps, published in the Journal of Gas Lighting, Volume 74, page 1055, and one by Mr. C. C. Carpenter in the same journal, Volume 70, page 1054, it seems that little or no benefit was derived from regeneration, equal or better results being attained, both financially and as to fuel account, by preheating the secondary air without the use of the heat from the "waste gases." These results as to cost, I believe, were on account of the cheaper construction of the part of the bench for preheating the air, as compared with recuperators, and possibly also to heating the secondary air to a greater degree than was accomplished by recuperators, and to the even distribution of the heat throughout the setting. I do not understand the failure of regenerative benches to show an advantage in the fuel account, unless it may be due to the last mentioned causes of greater degree of preheating secondary air and better distribution of the heat in the benches without the regenerators. The preheating of the primary air is, I think, somewhat open to question, inasmuch as steam is used under the grate in order to keep the temperature in the fuel bed, at least in the lower part. of it, where the proportion of ash is considerable, below that at which the ash would agglomerate into a hard clinker. The amount of steam used should be as low as consistent with the desired effect on the ash, as the steam tends to lower the temperature of combustion, not only in the furnace, but the secondary combustion as well. The combustion of the hydrogen formed from the steam probably tends to localizing intense combustion close to the nostrils, giving a less even distribution of heat through the oven than the combustion of the furnace gases without hydrogen. The specific heat of steam being higher than that of the other products of combustion, steam would increase the waste heat in the gases passing up the chimney. Again, the steam being formed from water, there is the unrecuperated heat of evaporation. It may be argued that the water may be evaporated by the products of combustion on their way from the primary air recuperator to the chimney. Is it not better, however, to evaporate the water by heat from the grate, because in this way the amount of steam formed would seem to be more nearly the amount needed, more being formed just after clinkering or pricking up when the grate is hottest, and less as the grate and material on it become cooled. By evaporating the water with the heat of the waste gases a nearly constant amount is formed in a given time, and to effect the desired results on the ash this amount must be the maximum required; consequently, as the lower portion of the fuel bed becomes cooler and the accumulation of ash hinders the passage of the primary air and steam, the primary air will be decreased, but the amount of steam remaining the same would tend to lower the temperature in the furnace more than required. About 30 pounds of water evaporated per 100 pounds of coke used in the furnace is usually sufficient to prevent the formation of troublesome clinker, but this would vary somewhat, depending upon the character and amount of ash in the fuel used. Sometimes it seems that a bench does good work in fair weather, but not as well during a foggy or rainy spell. Is this not at least partly explained in the following? Suppose the air at a temperature of about 60° F., and half saturated with water vapor, and the total steam passing through the fuel bed to be 30 pounds per 100 pounds of coke burned. Again, suppose the day to be foggy or rainy, so that the air is saturated with water vapor. In the second case the introduction of vapor by the primary air will be increased by nearly 31⁄2 pounds per 100 pounds of carbon burned in the furnace, or an increase of 11 2-3 per cent. in the amount of steam passing through the fuel bed, and assuming the same increase of 31⁄2 pounds carried in by the secondary air, we have nearly 21 per cent. increase in steam passing through the setting, the amount in the first case being 30 pounds through the fuel bed and 31⁄2 pounds. with the secondary air, making a total of 331⁄2 pounds. DISCUSSION. THE PRESIDENT-Mr. Slater's interesting paper is before you, and I have no doubt it will bring out a very interesting discussion. MR. ODIORNE-I would like to ask Mr. Slater whether he is using full-depth or half-depth furnaces of this character? MR. SLATER-We are using full-depth and have recently had very fair results. We have been using, as near as I can get at it, in benches of nines, about 23 per cent. of the coke we make in the furnace as fuel. We use it in benches of nines. MR. ODIORNE-My experience has been with the use of the half or semi-regenerative benches. I have used as fuel slack or dump from the coal mines, which we can procure very cheap. I find it a great saving over the use of coke. We can do the firing with this slack at less than one-third the present price, which we are obliged to pay for this. Formerly we got this slack simply for the hauling, but later we had to pay one cent per bushel for it, and recently we were told that the price was to be advanced to two cents per bushel. Even at that, however, its use will prove very much cheaper than firing with coke. I have a few figures regarding it which may possibly be of interest. The cost of firing with coke for 24 hours was $3.05; we used 2,457 pounds, or 61 bushels. Firing with slack we used 3,872 pounds, or 46 bushels, costing, at two cents per bushel, 92 cents, a saving of $2.13 per day. I made the test for 30 days, and figured it for that time. During this test very near the same amount of coal was carbonized in the retorts. It is not a large yield per bench, being about 42,676 feet, or about 7,102 feet to the retort. As these benches have been in use for about 21⁄2 years they are not to be considered as new ones. They did better of course when they were new. MR. DOTY—The subject of bench firing is attracting considerable attention among gas engineers to-day, who are impressed with the necessity of increased economies. I believe that Mr. Henry Doherty is the father of the suggestions for using mechanical stokers for bench firing, and the reasons are excellent. The uniform firing load makes the use of mechanical stokers a distinct saving. I understand from Mr. Slater that the Milwaukee Company has in use mechanical stokers for bench firing, and one of the stokers, I understand, is applied to the regenerative benches. It would be interesting if Mr. Slater would give to the Association the benefit of some of his experience in connection with the application of mechanical stokers to regenerative benches. The character of the flame from the stoker must be different in the main from the long coke or coal flame. Then, the application of the heat is different. I, for one, would be very much interested indeed in knowing why, in Mr. Slater's opinion, the stoker is of practical advantage. THE PRESIDENT-I think it will be better for us to understand that the writer of the paper will not answer the questions until the discussion is through, so I will consider, if no objection is made, that such course will be pursued. MR. EGNER-It seems to me that Mr. Slater is using a great deal too much water under the benches, and that perhaps if he used considerably less he would get better results. In fact, it seems to me, he is using nearly twice as much as is necessary. MR. FORSTALL-Mr. Slater refers to the English idea that recuperation does not pay. The English have spent 15 or 20 years discussing the subject and have not yet arrived at a conclusion. Some say that recuperation does not pay, and others say that it does pay. |