This article was originally published in Electrochemical and Metallurgical Industry Publication of October 1907. Information within this article is therefore correct as of 1907. The publication of this material aims to provide historical insight on the subject and its place in industry.
The utilization of peat is one of those subjects in which a host of investors have interested themselves and much money, ingenuity and energy has been spent to lead this intricate problem towards a solution. One of the most active workers in this field for a long series of years has been Professor A. Frank of Charlottenburg-Berlin, the same German chemical engineer who distinguished himself many years ago by his active work in introducing potassium salts into agriculture and quite recently by inventing, together with Dr. Caro, the process of making calcium cyanamide from calcium carbide. Anything that this successful engineer has to say on the difficult problem of peat utilization should, find most careful attention, especially as the matter will most likely become of great importance in future in this country.
This article is based on five papers, kindly sent to us by Dr. Frank. It is very interesting to see how the methods of utilizing peat have been gradually worked out, until now finally the commercial stage appears to have been reached.
In the Northern climate peat deposits are formed wherever stagnant water can accumulate. Peat is an accumulation of decayed vegetable matter, its decomposition still going on. The decay of the vegetable matter is an effect of the water, and first takes place in presence of air while in later periods air has no longer access to the forming peat. That the formation of peat is still going on is shown in places by observing an actual growth of the peat deposits in the course of years.
Fuel Made from Peat
To understand the possibility of using peat for industrial purposes it is necessary to consider its composition. This varies greatly with respect to the content of water, the content of ash, the content of nitrogen, etc., but the "peat substance" proper, that is, the pure organic substance of the peat, has a rather uniform composition, namely, 60% carbon, 5% hydrogen, 3% oxygen.
The water and the ash in the peat are simply obnoxious. The content of nitrogen may be made use of for the production of useful nitrogen compounds. On the other hand, the composition of the peat substance shows that it represents a storage of energy, since carbon as well as hydrogen when oxidized set free considerable quantities of heat. Peat deposits, therefore, represent enormous quantities of stored-up energy.
The difficulties in recovering the energy stored in peat are due to the composition of the peat and to its structure. Peat always contains large quantities of water. Although the water may be reduced by previous trenching of the area, yet the content of water in peat should be always assumed as 80-90%, and it becomes necessary to further reduce it artificially. The use of mechanical pressure to remove the water has not been found satisfactory. On account of the porous spongy structure of the peat, these are formed quickly under pressure impervious layers on the outside of the pressed volume, so that further removal of water is prevented. The same difficulty is found when the water is removed by sucking off or by the recently proposed method of electric endomosis. In any case so much power is required that the method is not economical.
The best method is always to first dry the peat in air, as was done already 2,000 years ago as recorded by Pliny. It has been proposed to combine this method of drying in air with a subsequent artificial drying by heat, the product being called "darrtorf," or to dry peat to a water content of 50-60% and then compress it, the product being called "trocken-presstorf." Dr. Caro thinks that neither of these methods is necessary, since it is possible to get quite satisfactory results by natural drying in air alone.
If the natural peat is directly dried in air the process takes a long time and the product is porous, hygroscopic and brittle, containing about 20-25% water and having a low specific gravity; i.e. there is little fuel per unit of volume.
Better results are obtained by the use of peat milling or crushing machinery. If in such machines the fibers are torn apart and the peat is kneaded, compressed and mixed, a uniform product is obtained which dries more quickly than natural peat and has a much denser structure, so that a solid cohesive product of comparatively high specific weight and a content of 15-20% of water is obtained.
"Machine peat" prepared in this way represents quite a satisfactory fuel which may be used for all purposes of heating. One kilogram of such peat may evaporate 3.5 to 4.2 kg of water. Wherever the use of such peat as fuel has failed a wrong construction of the furnace has been at fault. The dimensions must be quite large on account of the comparatively low heat value of peat, and air must be supplied in proper amounts in order to secure complete combustion and permit the escape of the water which is in the peat and which forms during the burning process.
Nevertheless, peat is an inferior fuel, and the use of peat as fuel must always be restricted to certain localities where other fuels are expensive. There is no possibility of peat competing with coal, though the latter sells at a fair price.
Dry Distillation of Peat and Production of Peat Coke
Since peat represents chemically an intermediate stage between wood and bituminous coal it was to be expected that dry distillation of peat would yield a satisfactory coke together with tar, ammoniacal liquor and acetic acid as byproducts. When peat is subjected to dry distillation, that is, under absence of air, water is formed from oxygen and hydrogen in the peat itself. Further oxygen and carbon in the peat combine to carbon monoxide and carbon dioxide, and finally hydrocarbons are formed from carbon and hydrogen in the peat. These products are distilled off and the balance of the carbon which remains back forms the coke. The first experiments were made, as in the distillation of wood, with "meilers," but these were not satisfactory. Better results are obtained with coking the machine-peat in closed retorts heated from the outside. The coke thus produced is rather hard, and the gas has such a calorific value that all the heat necessary for the distillation is provided by the gas. Further acetic acid and ammoniacal liquor are obtained.
A system which treats peat in this way is that of Ziegler, which has proven satisfactory and profitable in a plant in Oldenburg, while a similar plant in Rjedkino in Russia has been unsuccessful. The success of such undertakings depends on many factors, and greatly on local conditions. The price of peat coke depends on its purity, that is, on the quantity of impurities in the raw peat. In his lecture, 1907, Dr. Frank exhibited some samples of Ziegler peat coke from the new Upper Bavarian Coke Works in Beuerberg, and stated that this coke was of very satisfactory quality and would be a good substitute for charcoal. Nevertheless, the Ziegler process requires a rather pure peat, very low in ash, as raw material, and the necessity of preparatory treatment in machines is a disadvantage.
Peat Gas Producers and Generation of Power
The processes which we have considered so far relate to the application of peat as fuel, either in the form of peat fuel or peat-coke fuel. In any case, it is important to first dry and compress the peat for these purposes down to somewhat like 20% of water. Further, if one wants to produce good peat coke, one is restricted to the use of peat low in ash as raw material. Such processes may be profitable at certain places under local conditions, but they do not represent the solution of the general peat problem.
Professor Frank attempts this solution in another way. Instead of trying to subject peat to a treatment that would make it available for shipment to industrial centers, he says we must endeavor to bring industry and commerce into the peat-deposit districts. Peat areas should be considered just like waterfalls, as centers of stored-up energy. In his first paper (1897) Frank considered the erection of large generating stations in the peat districts with reciprocating engines, the peat being used as fuel under boilers. But even in those early days Frank considered that it might be possible to gasify' the peat in gas producers and use the gas directly in gas engines. This idea was taken up more strongly in his second paper (1903), since the large gas engine operated by producer gas, blast-furnace gases and coke-oven gases had made its appearance in the meantime in the industry. In this paper he estimates that in a gas-engine plant it is possible to produce about twice the amount of power which can be produced from the same amount of peat in a steam-engine plant.
In this paper (1903) it is also mentioned that the generation of a suitable producer gas from lignite and peat has been proven practical, that lignite gas engines are operating at the Mansfeld Gewerkschaft, near Eisleben, and on the Sophien mine, near Meuselwitz, and that peat gas engines have been built by the Deutz Gas Engine Co. by Koerting Bros. by Julius Pintsch, by the Oberursel Machine Co. and others. The Deutz Gas Engine Co. reported that when using air-dried peat, containing 16.57% water, i-hp. hour requires 1.27 kilogram of peat, while according to a later statement the same company has succeeded in reducing the quantity of peat required for I-hp hour to 0.85 or 0.9 kg.
But what is still more important, it is by no means necessary in such processes to dry the peat to such an extent that it contains only somewhat like 20 per cent of water. It is quite possible to gasify peat containing 50-55% of water. Moreover, in this process, it is possible to recover almost the total nitrogen contained in the peat in form of ammonia.
On the basis of the well-known Mond process, Dr. Caro has worked out a new method for gasifying peat in a mixture of air and overheated steam in excess. This process has been tried with Irish peat on the Mond works in Stockton, and it has been found that almost the total amount of nitrogen in the peat is changed into ammonium sulphate, which can be easily sold as fertilizer.
At the Stockton works the output from 100-kilogram peat, calculated as free from water and containing somewhat more than I per cent nitrogen, was 2.8 kilograms ammonium sulphate and 250 cubic meters of producer gas with a calorific value of 1,300 calories.
Dr. Caro gives the following results obtained in tests in Winnington, England, where there is a large Mond gas producer plant. The Mond gas producers which were available there were partly used for gasifying peat. The peat gas was supplied to the gas engines which were otherwise operated with Mond gas, and ammonium sulphate was recovered in the same works.
The engineer in charge of the gas engine plant did not know whether he received Mond gas or peat gas, because all gas came through the same supply mains. He did not even find the difference in the operation of the gas engines. Italian peat was employed in these tests since they were made in the interest of a projected works in Italy.
"Six hundred and fifty tons of peat were gasified in the whole. The composition of the peat substance, assumed free from water, was ash 15.2%, volatile substances 43.8%, nitrogen 1.62, total carbon 56.3, fixed carbon 34.2, with a calorific value of 5,620 large calories. The peat was used in different conditions, mostly with an average content of 40% water, and 1,780 cubic meters of gas with a calorific value of 1,360 large calories were obtained per ton of water-free peat substance.
Besides this there were obtained 118 British pounds = 55 kilograms ammonium sulphate per ton of water-free peat. I state again that this was not ammonia gas, but real salt which was weighed.
"The gas was partly used for generating the steam required for the gas producer process, partly for heating the ammonium sulphate solution, and besides this an excess of gas was obtained, namely, for each ton of water-free peat gas was obtained giving 480-hp hours in gas engines.
"In this plant the cost of the treatment of roo tons of peat (the weight being calculated on the basis of water-free peat) was $50, including wages ($1 to $1.25 per man per day), repairs, etc. Further, for the production of the ammonium sulphate, sulphuric acid, costing $41.25 (at $7.50 per ton), was used. Finally, if the amortization is taken as $33.75 (at 10%), the total cost is $125. On the other hand, from these 100 tons of water-free peat ammonium sulphate in the amount of about $325 was obtained. This shows a good profit, especially if it is considered that the gas is supplied to the gas engines in absolutely pure condition.
"It has been found that the segregation of dust particles in a gas which has been freed from ammonia, takes place with much greater speed and intensity than in peat gas containing tar. One cubic meter of gas contained only 0.16 gram of tar, and the gas engines operated with this gas very well and without trouble. The content of hydrogen in the gas does not vary more than 4% in the maximum.
"The cost of the 480-hp. hours produced was, of course, very low. If we do not take into account the profit from the ammonium sulphate the cost of the electric horsepower-hour was less than 0.125%"
Finally, peat gas produced in this way is not only suitable for generation of power, but may be used for all kinds of heating purposes if proper furnaces are employed. Its use in steel works recommends itself, since it is absolutely free from sulphur.
In order to test the process in the interest of German industry, an experimental plant is being erected on the Mont Cenis mine in Sodingen, in Westphalia, as was already mentioned in our April issue, page 145, for the treatment of waste coal and peat. If successful, the chief result will be the use of wet non-briquetted peat in gas producers for the generation of cheap power and the production of ammonium sulphate.
The income from the latter alone is expected to assure a fair interest on the capital; $187,500 is given as the capital invested in this plant. The results of these tests will certainly be awaited with interest.
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