Bericht Ironhirst

Aus dem Bericht von J. O. Roos of Hjelmsater, Director of the Govern­ment Testing Laboratories in Stockholm aus.

Schreibweise möglicherweise Roos af Hjelmsäter, der Name einer alten Adelsfamilie.

in Teknisk Tidskrift / 1938. Väg- och vattenbyggnadskonst / 46
als Statens Provningsanstalt: professor John Roos af. Hjelmsäter

4. Roos af Hjelmsäter, J 0: Torvkoltillverkningen vid Dumfries.
Skottland. Tekn. T. 50 (1920) s. V 181.


Governments of the Dominion of Canada and the Province of Ontario
PEAT -Its Manufacture and Uses


Hinweis: Die erwähnte Zeichung ist im Orginal leider nicht gescannt worden. Die Tabellen müssen noch umformatiert werden.

The syndicate built a small plant at Dumfries, Scotland, and continued experi­mental work until 1911. In 1912 a new company was formed, called Wet Carbonizing, Limited, with a paid-up capital of £250.000. The capital of this company in 1919 was £1.000.000 of which £900.000 was paid up.

During the first years of the war the plant was closed down, no com­mercial success in production of fuel or recovery of by-products having been attained, although very heavy expenditures had been made over a period of several years.

The Ministry of War, having found that the wet-carbonized briquettes were a smokeless fuel and, therefore, particularly suitable for use in the trenches, took over the property as it stood in 1917, and, with the benefit of the experience gained, erected a new plant, designed on a large industrial scale, for the production of 60,000 tons of briquettes per annum. The new plant, which was well designed and thoroughly equipped, and built at the expense of the British Government, was not completed until after the close of the war, when it was turned over to the company for operation, and regular manufacturing of fuel was begun in October, 1919.

Operation of the plant was made feasible by the utilization of slack coal as fuel, the maximum price for which, under government regulations prevailing at the time, was fixed at 30 shillings per ton, and owing to the heavy demand for fuel, the briquettes produced could be sold, free from restriction, at 90 shillings or more per ton.
In November of the same year a Swedish Government Commission visited the plant, special trial runs were conducted and a report on its operation was made by J. O. Roos of Hjelmsater, Director of the Govern­ment Testing Laboratories at Stockholm, which affords the following data:

  • Estimated production of briquettes: 60,000 tons per annum.
  • Actual pro­duction: 130 tons per 24 hours, or 40.000 tons per annum.
  • Number of men employed: 250.
  • Volume of buildings housing plant, approximately 1.650.000 cubic feet.
  • Power requirements: 1.050 kilowatts.
  • Comparative fuel value: 1 ton briquettes equal in effective value to 0.65 ton best English steam coal.

The decisive factor, however, which determined the economic value of the process, was the very large heat requirement. Observation of production of briquettes and consumption of fuel during the 24-hour periods of regular operation showed the following results.

  • Briquettes made, Coal used,
  •                     tons tons
  • First 24-hour period 132 114
  • Second 24-hour period 140 12
  • Average per 24 hours 136 121

Analyses gave an effective calorific value of the briquettes of 4,380 calories as against 5.300 calories for the slack coal used. The average number of effective calories produced and consumed daily were:
Briquettes made 696.000.000 calories

Coal consumed 641.000.000 “


J. O. Roos, Director of Government Testing Laboratories, Stockholm, Sweden
Martin Ekenberg, a Swedish engineer resident in London, was the inventor of a wet-carbonizing process for treatment of peat, which was tried out experimentally at a plant at Stafsjo, Sweden, and which was later on closed down.

After his return from Sweden, Ekenberg, in 1907, formed in London a company known as “The International Carbonizing Company, Limited,” with a nominal capital of £41,000. The amount actually paid in possibly did not exceed £500.

With the object of developing Ekenberg’s inventions, a Swedish merchant, Nils Testrup of Newcastle, later formed a syndicate with a paid- up capital of £35.000. This syndicate built a small wet-carbonizing plant according to Ekenberg’s designs, and continued experimental work until 1911. At that time the syndicate had expended £150,000.

Eken­berg died in 1909, and was succeeded by his assistant, Olaf Soderlund.
In 1912 a new company was organized, called Wet Carbonizing Limited, with a paid-up capital of £250,000. The main shareholders of this company at present are Lord d’Albernon of the Ottoman Bank, Messrs. Arthur and Gerald Balfour, Joseph Fels, Crossleys of Manchester, and Nils Testrup. The capital has gradually increased, and was in 1919, £1,000,000, 7 per cent preferred shares and about £10,000 common, of which £900,000 has been paid up.


In order to carry out Ekenberg’s inventions on a commercial scale a small factory was erected in 1909, at Dumfries, on a large area of peat bog rented for the purpose. In this plant the details of the process were worked out until the mechanical difficulties had been generally overcome. At the outbreak of the war the possibility of a continuous process of manu­facturing carbonized peat briquettes had been demonstrated. During the first years of the war all work was closed down, but the Ministry of War finding these briquettes to be a smokeless fuel and therefore especially suitable for use in the trenches the government took over the plant as it stood in 1917. This plant had been designed for recovery of by-products— ammonium sulphate, tars, etc.—as well as manufacture of briquettes and as the government was particularly interested in the production of peat briquettes, a new plant was erected, which was designed, in the light of experience already gained, especially with a view to manufacture of briquettes.

The plans for this new plant were on a large industrial scale for the production of 60,000 tons of briquettes per annum. It was built at the expense of the Government during 1918 and 1919, and when completed was turned over to the company in September, 1919, under an agreement for payment within a period of ten years according to valuation. Opera­tions were begun in February 1919, but, owing to somewhat extensive alterations, delays due to the railway strike, etc., it may be considered that an actual start in manufacturing was not made until October, 1919, when a daily production of 130 tons of briquettes was reached, equivalent to an annual output of 40,000 tons. The management of the company believe that by comparatively small changes in construction particularly in the wet-carbonizing tubes, the estimated annual production of 60,000 will be eventually reached.

Zitat •Tra slat n by H. A. Leverin, Chemist, Mines Branch, Ottawa, from Teknisk Tidskrift, April 17,1920.


The company is operating on a bog area consisting of two parts, Ironhirst Moss with an area of 600 acres, and Racks Moss covering 1.200 acres, situated near each other a few miles from Dumfries. The bogs are rented for a long term of years on a royalty of 3 d. per ton with a minimum annual payment of £400. They contain a fuel peat of fair quality, partly grass peat at the surface, and reed peat farther down, and are fairly free from stumps excepting at the bottom where some oak stumps occur. They are exceptionally deep, being 7 to 9 metres with an average depth of 7 ,5 metres, and are undrained, the water-level being from 0,3 to 0,5 of a metre from the surface. The undecomposed surface peat represents about 6 per cent of the total volume. Analysis gives content of:

  • Ash 5-0
  • Sulphur 0-85
  • Phosphorus 0-002
  • Nitrogen 1,45 Per cent

Calorimetric values are:

  • Surface peat 4,925 calories
  • Bottom peat 5,255 “
  • Average 5,120 “


The factory is 1 kilometre from the edge of the bog and about 10 kilometres from Dumfries on the Glasgow-Carlisle Railway, with a spur in to the works. The object of the process is to be independent of air-drying. The method is to remove part of the water by pressure and the remainder by air-drying, thereby obtaining a peat powder with low moisture content which can be pressed into briquettes. Owing to the special war conditions it was desired to obtain as great a production of briquettes as possible, consequently coal slack was used as a fuel for carrying on the operations.
Pressing does not remove a great deal of the water from raw peat unless its colloidal properties are first destroyed. This is accomplished by the wet-carbonizing process under which the raw peat slop is heated in a system of tubes to about 200° C. under corresponding pressure. During, the process the peat slop is partly carbonized, the organic structure ispartly destroyed, it loses its colloidal character and can be pressed in ordinary filter-presses to about 30 per cent dry substance, and by means of hydraulic presses to 50 per cent dry substance. The remaining water is evaporated by heat supplied by the waste gases from the power plant. The mechanical devices required for this process consist generally, of the following, as shown on accompanying diagram (Figure 46):

Excavator: On the bog with pumping system to move the peat slop to the factory.
Peat Reservoir: For storing an amount of raw peat sufficient for two days’ production.
Liming Apparatus: For adding lime to neutralize acids formed during wet-carbonizing.
Pumping Plant: For transportation of the peat slop to the wet-carbon­izing tubes.
Wet-carbonizing System: For heating the peat slop to 200° C. for a sufficient length of time, and for recovery of the heat by reverse flow method.
Filter Presses: For pressing the wet-carbonized peat powder to 30 per cent dry substance.
Disintegrators: For pulverizing the pressed cakes and sifting the powder.
Drying Plant: (Rigby system) for drying the peat powder by means of waste gases from the power plant, obtaining the bulk of the dry powder in so-called cyclone chambers, and the remaining dust by scrubbing the gases.
Briquetting Plant: For pressing the dry powder into briquettes.
Power Plant: Generating electric power for all requirements.
Loading and Unloading Appliances: Including a railway spur for unloading of coal and loading of briquettes.


Excavator (A, B, C, D)

The excavator consists of a floating dredge, macerator, root remover, and pumps for transportation of the slop to the factory. The excavator plant was erected at the edge of the bog. It floats on a pontoon 33 metres long, 12 metres wide and about 1-8 metres deep with draught of about 1 • 4 metres. The pontoon is kept in place by steel ropes anchored on the shore, also by means of supports from the stern against the bottom of the bog. By manoeuvring these lines by motor control the dredge works on the arc of a circle on the edge of the bog. The excavator proper consists of an elevator with scoops holding about * ton each, excavating at a speed of about 40 scoops per minute. The scoops cut the bog side­ways in two layers. They are as a rule only half-filled, and raise on an average about 300 tons of wet peat per hour, corresponding to 18 tons of dry substance per hour. The excavated peat is dumped into a hopper where a root remover of special construction is installed removing average­sized roots and stumps which are thrown back into the excavation. Larger stumps and roots must be removed by hand from the buckets in motion.

Addition of Lime

The raw peat contains certain humous acids which during the process of wet-carbonization are changed into other acids such as formic, acetic, oxalic, and others.

These acids attack the wet-carbonizing tubes, and must therefore be neutralized. This is accomplished by the addition of slaked lime in a special apparatus before the peat enters the macerators. It has been found that the most suitable amount of lime to be added is 3 to 4 per cent of the dry substance of the peat. The lime increases considerably the ash content of the peat powder, and also causes deposition of oxalate of lime in the wet-carbonizing tubes, which will be dealt with later.

Elevator and Storage Tower for Raw Peat (H)

From the macerators the peat slop is elevated into a small storage tower from which it flows to the pumping system.
Pumping System (K)
In order to pass the peat through the wet-carbonizing tubes at a certain speed, and to resist the steam pressure of 200° C., a pump pressure of about 40 atmospheres is required, which is produced by a series of motor-driven pressure pumps. Each motor drives by means of gear wheels two symmetrically lying pumps each with two pistons. Each piston feeds a wet-carbonizing tube. There are five such systems each consisting of one electric motor, two pumps of two pistons each, and four wet-car­bonizing tubes. Each motor requires about 70 kw. The number of men required for the pumping plant is six for each shift. The plant is especially well designed and functions with great regularity.

Wet-Carbonizing System (L,M,N,O)

n this plant the object is to heat the peat mass to 200° C. for a period of 18 minutes, and by employment of reverse flow recover the greater part of the heat, so that the water pressed out will be of only slightly raised temperature, compared with the original mass. The temperatures mentioned below were obtained at wet-carbonizing tube No. 17, and checked by me. The plant consists of five systems each of four units. Below, one such unit is described. The raw peat is pressed through a tube of 4 inches outside diameter and j to f inch in thickness, and of very great length, which passes through three different stages of heating.

The Water Regenerator (L)

The inner tube is surrounded by a cast iron pipe of 13 centimetres inside diameter. In this outside tube the water pressed out from the filter presses runs by its own pressure in the opposite direction to the movement of the peat slop. The length of the water regenerator, which is arranged in coils, is about 67 metres. The present plan of conducting the filtered-out water through the tubes by its own pressure has not proved satisfactory, as only about 3 tons of water per hour passed through the tubes, whereas the total amount of water pressed out from the peat amounted to 9 tons per hour. Consequently the efficiency of heat recovery obtained was low. (Temperature of raw peat entering the system 8 • 2° C. and leaving the system 21-6° C. Temperature of water entering 58-9° C., and leaving 19 -3° C.) The water after regeneration was allowed to run out on the bog, as well as a large amount from the filter presses, that could not pass through the tubes.

The Warm Peat Regenerator (M)

In the warm peat regenerator the inner tube containing the raw peat is led through a steel tube of 13 centimetres inside diameter. In this outside tube the warm peat slop from the reaction tower moves in the opposite direction to that of the raw peat. The length of the warm peat regenerator is 243 metres, lying horizontally in a coil of four lengths in the open air. These are surrounded by an insulating cover of slag wool and corrugated sheet metal. Temperature of raw peat entering 21’6° C. and leaving 138*9° C. Temperature of warm peat entering 197*4° C. and leaving 74*1° C.

When it was discovered that the acids formed during wet-carbonizing attacked the iron tubes, their length of life being only three to six months, it was found necessary to neutralize with lime. It was then found that lime salts at the lower temperature precipitated on the walls of the wet- carbonizing tubes. The deposit so formed consisted generally of oxalate of lime, which was rapidly formed of such thickness that the conduction of heat between the warm and cold peat slop became so poor that the cal­orimetric efficiency was appreciably reduced. It became necessary to scrape the inside and outside tubes every fourth day. This from the point of view of continuous operation is most unsatisfactory, as it requires 5 to 7 men per shift for that work. Experiments are being made with a view to minimizing these difficulties.

The Steam Jacket (N)

The inner tube with the preheated raw peat next is led through a steam jacket 31 metres long through which it passes in coils of four, and in some systems six, having therefore a length of 126 or 200 metres. This steam jacket is supplied with steam at 205° C. from the boilers, and raises the temperature of the peat to about 200°C. Temperature of incoming peat was 138,9°C. and outgoing 199,9°C.

Reaction Tower

In order to obtain effective carbonization at 200° C. the peat mass must be kept at that temperature for about 18 minutes. This is done by leading the heated peat into a cylindrical tower of steel plate lined inside with clinker. (Inside diameter 1 • 2 metres, height 4 • 5 metres) where the peat passes through a number of levels from below upwards being kept in motion by a central stirrer. The outgoing temperature from the tower was 197,4° C. Capacity of the tower about 10 tons per hour. At the time of my visit 9 tube units were in operation, but the plant would permit operation of 12 units (3 systems). Besides these, 8 units were in process of being cleaned. The warm wet-carbonized peat flows through the outside tube of the warm peat regenerator to the warm peat reservoir. This consists of three cylindrical tanks with a capacity corresponding to a couple of hours run, where the gases formed are taken off and from which the peat mass under pressure of 7 to 8 atmospheres passes into the filter presses. The temperature in the warm peat reservoir was 74-l°C.

Filter Press Plant

There are eleven presses each of 94 frames making press cakes 50 inches by 50 inches. In order to obtain a favourable pressing a temperature of at least 76°C. is required. The actual temperature was 74°C. Using a pressure of 100 pounds per square inch a press cake was obtained with very constant dry substance content of 30 per cent. Each pressing by one press produced about 7 tons of press cakes equal to 2-1 tons of dry substance. Each operation of the press took about 2| hours. The press cakes were removed by hand. The filter presses are of cast iron and of standard type, and the filter cloths of ordinary canvas. Seven men per shift were required making 60 pressings in 24 hours. The press cakes drop through a breaker (R) on a belt conveyer (S) which brings the material to a disintegrator (T) and to centrifugal mills (U) for pulverizing. The powder is conveyed for drying to a storage room with sloping bottom (V). The water extracted by the filter presses is led through pipes to the outer tube of the warm water regenerator in order to give up its heat to the incoming raw peat. Owing to unsuitable arrangements there is a considerable loss of heat in the filtering process through formation of steam by which the temperature of the water pressed out was lowered from 74°C. to 58,9°C. From a mechanical point of view the filter presses functioned satisfactorily and with regularity.

Drying of Peat Powder

The drying of the peat powder is effected by the Rigby process in the following manner. The moist powder is brought to the mouth of a large insulated boiler plate cylinder, 1 ,8 metre in diameter and 200 feet long, where it is caught up by the waste gases from the power plant which are forced through the tube by fans at an incoming temperature of 300°C. to 350°C. Owing to their carbonic acid content (about 10 per cent) no ignition will occur below 700°C. Owing to their speed the gases pick up the peat powder. The volume of gases and the amount of peat powder are so proportioned that at the other end of the cylinder, the temperature is about 85°C. and the moisture content of the peat powder 8 per cent. In order to separate the dry peat powder the gases are led at high speed through the so-called cyclone chamber (h) where the peat is deposited, and by a conveyer brought to a storage hopper over the large briquetting presses (c, d, e, f, and g) in which it does not remain long. The gases leaving the cyclone chamber are led through a water tower where any remaining peat dust is washed out and returned to the filter presses. The drying system, from a mechanical point of view, functioned satisfactorily and with great precision. On the other hand it was found that the loss of peat powder remaining as dust in the gases was considerable, estimated at 10 per cent.

Briquetting Plant

The installation directly follows that of the German brown coal briquetting plants, and two of the machines were of standard type from the firm Maschinenbaugesellschaft Buckau, Magdeburg. During the war a large press was built in England, so they now have three of them, two large and one smaller. These presses are driven according to the German system with steam of 5 atmospheres, and a back pressure ofabout \ atmosphere. The exhaust steam could not be utilized. The briquetting presses worked very satisfactorily, the smaller one delivering 2 tons and the large one 3 tons per hour. One press was held in reserve. During November the output was about 125 tons of briquettes daily. Labour requirement was 3 men per shift.

The Boiler Plant

This consisted of 4 Babcock and Wilcox boilers, each of about 3,400 square feet heating surface producing 15,000 pounds of steam of 300 pounds pressure per hour. They were supplied with chain grates and were fired with slack coal. Three were kept in operation and one in reserve. The waste gases were led by fans to the drying plant. As these were not sufficient for the drying of the powder with 70 per cent moisture, there was also a small furnace where coal was burned directly, the gases from which at high temperature were mixed with the gases from the boiler plant. Labour required, 6 men per shift. The boiler plant was built in one of the earlier stages and the removal of ashes and slag was awkward, requiring an unnecessary amount of labour.

The Power Plant

All power required was supplied from two steam turbines of 1.700 kw. from the firm Beliss-Morcom, Ltd., Birmingham. Steam pressure 300 pounds, condenser pressure 28 inches of water. One of the turbines was held in reserve. Energy transmitted to the larger motors was supplied by an A.C. generator, from the British Electric Company, of 3-phase current at 3,300 volts tension. For the smaller motors this was transformed down to 440 volts. The total power required with the present output of 40,000 tons per year was a maximum of 1,050 kw. divided under the following headings:

  • Excavator 250 to 300 kW.
  • Pumps and wet-car bonizer 160 kW.
  • Fans for drying 240 kW.
  • Condenser for turbine 100 kW.
  • Other purposes 300 to 250 kW.

Size of Buildings

In order to give an approximate idea of the size of the plant, the approximate size of the various buildings is stated in the table below. Most of these were united to form a large complex. Materials used in most cases were steel and corrugated plate. A few of them had brick walls.

Name of building Approx.
length Width Height to eaves Approx.
House for macerators, etc
Wet-carbonizing pump house
Heating house
Heating house
House for filter presses
House for accessories
House for pulverizing, etc
Cyclone chambers, etc
Briquetting plant
Power station, etc
Boiler house and accessories, houses
Briquette storage
Sundry small buildings Ft.
68-0 Ft.
41- 0 36-0 44-2 78-8
42- 6 46-0
36-0 Ft.
36- 0 23-0 39-3 18-0
37- 7 32-8 39-3 39-3 39-3 39-3 18-0 36-0 Cu. ft. 35,314 185,035 98,172
170.213 179,042
170.213 135,605 150,437



The original material, raw peat, has the colloidal or gelatinous property common to all fuel peats. By heating in water to a temperature about 200° C. under corresponding pressure a part decomposition of the organic substances occurs, which becomes more complete the longer it is subjected to this temperature. In this case 200° C. during 18 minutes was employed. Part carbonization takes place whereby certain organic matters are decom­posed, forming water, carbonic acid, oxalic acid, acetic acid, and other compounds. The remainder is the peat powder, which during the process has lost its colloidal property and permits of removal of the greater part of the water by mechanical pressure. By wet-carbonizing the peat mass loses in weight. In this case 87 per cent of the dry substance contained in the raw peat was recovered. At the same time the calorific value of the dry substance was somewhat increased, so that the recovery by wet- carbonizing amounts to about 92 per cent according to laboratory tests. The wet-carbonized and dried peat powder is pressed into briquettes which are the final product.

The Briquettes

These were of rectangular shape and made in two sizes:— Dimensions with the smaller press 120 by 70 by 18 mm.
Weight 2 kilograms Dimensions with the larger press 185 by 107 by 24 mm.
Weight 6 kilograms
The briquettes are black with a shiny surface and a brown, amor­phous break. To what degree they are able to stand storage in the open air, I have been unable to obtain any data. In a dry place, however, they can remain for a very long time without undergoing any appreciable change. They burn with a flame, and can be used advantageously in both open and closed fire-places. Owing to their regularity in shape and cleanness they are especially advantageous for domestic fuel. The ash depends, naturally, on the composition of the peat. In this case, owing to addition of lime, it was white in colour. The briquettes break slightly in firing and with very strong draught might tend to form sparks. Experi­ments are now being made on the Norwegian State Railways as to their use for locomotive fuel. As a general opinion it may be said that the briquettes appear to be a specially good fuel and easy to handle. The calorific value of the briquettes depends, naturally, on the ash content and composition of the raw peat. Analyses of wet-carbonized peat from different parts of the bog gave as an average:—
Raw peat 5,120 calories
Lime 4 per cent of the dry substance
Moisture of briquettes About 8 per cent
Calorific value of briquettes 5,435 calories
Samples taken by me during 48 hours’ trial run, and analysed at the Materials Testing Station at Stockholm gave from absolutely dry sample:—
Ash 9-8 per cent
Calorific value 5,150 calories
As delivered, ash 8-9 per cent
Moisture 9 per cent
Effective calorific value 4,380 caloriesThus, the calorific value of these briquettes was lower than the average figure given at the plant, which probably arose from the fact that at the time of my visit some part of the bog was being worked where the peat was of inferior quality. For purpose of comparison it may be stated that the best English steam coal (best South Yorkshire) as delivered gives the following average:—
Ash 5 per cent
Effective calorific value 7,000 calories


As all power and heat required at the plant were obtained from the use of slack coal under the boilers with a view to obtaining the largest possible amount of saleable briquettes, it was of great importance to obtain knowledge of the fuel consumption as compared to the amount of briquettes manufactured. No daily operating chart seemed to be kept. On that account the Swedish Commission arranged for a trial run of 48 hours in two periods of 24 hours each. Owing to favourable local condi­tions the amount of fuel used and briquettes produced could easily be ascertained with sufficient accuracy in the following manner. A certain number of railway cars loaded with coal were weighed on car scales and the figures checked. The boilers were fired with the coal from these cars after which the empty cars were weighed. During the first period of the trial run, one of the larger and the smaller briquette press, and during the second period the two large presses were in operation. The length of the string of briquettes was measured, and a number of 60-foot lengths of these weighed.

– —- Briquettes
made Coal
First 24-hr. period Tons
132 Tons
Second 24-hr. period 140 128
Average per 24 hours 136 121

General samples of the coal and briquettes were taken and afterwards analysed at the Government Materials Testing Station in Stockholm. Moisture content of briquettes as per analysis at the company’s labora­tories was 9 per cent. Analysis at Stockholm gave about 10 per cent. It is possible, however, that some water might have been absorbed in transportation.
Results of analyses at Stockholm on samples as delivered:—

— Briquettes Coal
5,150 calories 4,380 “ 11-4%
6.300 calories
5.300 “
Calorific value
Effective calorific value

From this is obtained an average number of effective calories per day:—
Briquettes made 596,000,000
Coal consumed 641,000,000
Results of this trial run show that practically as many calories were consumed as produced. This means that if instead of coal, the peat briquettes had been used as fuel for the plant, the entire output would have been consumed leaving no balance for sale. Notwithstanding this situation the plant might be kept in operation at a profit, or at least without any considerable financial loss, owing to the State regulation and control of prices for coal, which fixed a maximum price of 30s. per ton for slack coal, while the briquettes were sold free from restric­tion at a price of over 90s. per ton. That the directors of the company, to whom the unsatisfactory results obtained must have been known, should in spite of that invite foreign experts to inspect the plant was partly due to the fact that they considered that many complex mechanical problems had been cleverly solved, which is also my opinion, and that a plant like this for manufacturing peat briquettes according to the wet-carbonizing system must be considered a great step in advance; and partly because they felt convinced that by some improvements, and changes in details, a new plant could be built which would have a satisfactory efficiency.


The technical staff of the company have made calculations of the possible efficiency obtainable in a new plant designed for the production of 100.000 tons of briquettes for sale annually. These I was allowed to examine. In these calculations the heat losses of the projected plant had been figured in the most important details upon the assumption in every case that the heat-saving appliances used should be of the utmost efficiency which technical skill can produce. By combining these calcu­lated heat losses a result was obtained of 60 per cent efficiency, i.e., 60 per cent of the wet-carbonized peat could be sold as briquettes and 40 per cent would be consumed by the plant. Thus, the projected plant should have a gross production of 170,000 tons. To be able to figure out synthe­tically the efficiency of so complicated a plant is not in my opinion, feasible, since when put into actual practice so many unforeseen circumstances and conditions inevitably arise. The investigation has, however, in my opinion great value from the point of view that 60 per cent is the utmost limit of heat-efficiency which can be obtained from an ideally-built plant according to the wet-carbonizing system, and that the limit of practical efficiency must lie considerably below that point. From a study of the existing plant a number of details can be picked out where considerable improvements are necessary and even possible to produce increased effi­ciency. The most important of these are the following:

Steam Plant and Power Station

By burning wet-carbonized peat and dry peat powder under the boilers a much improved thermic efficiency can be obtained than under the present system of firing slack coal on grates. By replacing the present steam turbines which were not carrying a suitable load by the more economical Ljungstrom steam turbine better results should be obtained.

Wet-carbonizing System

A specially vital part of the plant from a heat efficiency point of view is the wet-carbonizing system where the heat is reclaimed in the warm water regenerator and the warm peat regenerator by reverse flow method. These as mentioned did not work satisfactorily. From the point of view of reclaiming heat as well as keeping them in continuous operation it is necessary that some arrangement should be devised to prevent deposition of salts in the tubes, which hinder the transmission of heat and cause difficulties in cleaning. At the same time the danger of acids attacking the tubes must be provided against. In order to obtain a better heat recovery it is proposed to lengthen the wet-carbonizing tubes from 800 feet to 1,480 feet, also the outgoing warm water must have a better circu­lation in the tubes of the warm water regenerator. By these changes a considerable saving of heat is possible.

Pressing Out of Water

This is probably the most important detail in the whole process. The whole idea of the wet-carbonizing process is so closely related to removing the water by pressure, that in order to prove effective, it should be possible to remove most of the water by mechanical pressure. In the existing plant the water could be reduced only to 70 per cent. The re­mainder of the water, i.e., 2-2 tons of water per ton of dry substance had to be removed by direct heating. An indispensable condition is that the water should be reduced to 50 per cent in the press cakes, so that only 0*9 ton of water per ton of dry substance need be removed by heat.

Experiments so far made with the object of constructing a continuous pressing system have failed, and it was considered that it would be better to press the pulverized cakes from the filter presses to 50 per cent moisture content in hydraulic presses using labour-saving machinery. By experi­ments this was found to be possible. Cakes weighing 5 • 5 kilograms were subjected to a maximum pressure of 120 kilograms per square centimetre. At each pressing 12 cakes were obtained in 25 minutes. Details for con­struction of such plant have not been worked out but it is evident that the plant will be very expensive, and will require a considerable amount of hand labour. It must also be borne in mind that the water pressed out from the filter presses, and which has to give off its heat to the incoming raw peat, lost 20° C. by open evaporation. This loss could be considerably lessened by suitable arrangements.

Drying of Peat Powder

In the final drying, according to Rigby’s method, by the waste gases from the power plant and the collection of the powder in the cyclone chambers there is considerable loss of dust, estimated at 10 per cent. This loss could also be considerably lessened.
Briquette Presses

The present presses are constructed for brown coal plants where the exhaust steam is used for drying of the brown coal. By using better steam-saving machinery, for instance the Uniflow Engines according to the Sulzer system, it was figured that the briquetting could be accomplished with use of less steam.

Possible Results of Heat Saving

By more suitable arrangements in other parts of the plant, it is believed that still more heat could be saved. The chief engineer of the company figured that by such changes the present plant could reach an efficiency of over 50 per cent. Whether this is practical in a plant where so many details contribute to the loss of heat, I consider most uncertain. An efficiency of at least 50 per cent is necessary in order that one could even imagine the possibility of such an expensive plant becoming a paying proposition.

It is evident that such changes as mentioned will involve a great deal of new construction and experimental work at heavy cost. This work ought to be done at the present plant at Dumfries, where they have the advantage of experience and their own patents. I must emphatically warn against any such experiments on a large scale at a new plant in Sweden. Such an enterprise without the resources which from a technical and mechanical point of view are obtainable in England would take too long a time and would require enormous expenditures of money which assuredly would be very difficult to recover.


As a basis for even thinking of applying the Dumfries method it must be assumed that it will have an efficiency of at least 50 per cent. The fol­lowing discussion, therefore, proceeds on the assumption of the improve­ments at the Dumfries plant being made, and its efficiency thereby raised from nothing to 50 per cent.

Cost and Size of Plant

As already mentioned considerable costly new construction is required and the units are very large. As a consequence the cost of the plant is very high in proportion to its production, and, as is generally the case in such complicated plants, the cost per ton of briquettes is higher for a small plant than for a large one. If we assume a gross production of 80,000 tons with the above efficiency of 50 per cent, this would yield 40,000 tons of saleable product per year. It is impossible to give with any degree of accuracy the cost of such a plant, partly because of new expensive equipment required, such as the proposed hydraulic presses for reducing the water content from 70 per cent to 50 per cent, and any estimate of cost must be largely guess­work. Estimating on figures obtained from the company, based on pre­war prices, a plant to give 80,000 (i.e. 40,000 net) tons production annually would cost in Sweden 12 to 15 million kronor, inclusive of bog, railway spur, and workingmen’s cottages. Assuming that cost of plant and working capital amount to 14 million kronor, this would represent a capital cost of 350 kronor per ton per year of saleable briquettes. For a smaller plant this cost will be higher, and for a larger plant somewhat lower. If we assume that the bog has an average depth of 3 metres with 92 per cent water content an area of 70 acres would be excavated per year, and for a20-year period 1,400 acres. It is apparent that only a very small number of bogs in Sweden would be suitable for such large production. It may also be pointed out that a considerable saving of labour is effected by the large floating excavator and the large pumping plants conveying the peat to the factory, and that the bog should be free from stumps and in such state that such an excavator can be used. Whether the wet-carbonizing system can be used for less well-humified peat, I am unable to give an opinion.

Winter Operation

It does not seem likely that the excavator can operate after the bog is frozen. Arrangements may be considered whereby excavation and conveying of the raw peat can be accomplished even during the winter, but until such problems have been solved, we must accept the fact that in Sm&land, for instance, continuous run for more than nine months is out of the question, which means reduction of output of saleable briquettes from 40,000 to 30,000 tons per year, and increase of capital cost to 470 kronors per ton per year.
Number of Men Employed
Cost of Production
At such a plant the number of men employed is estimated to be about 200, divided into three shifts. The actual number at Dumfries was 250, but a number of men were engaged in experimental work. Under Swedish conditions with 48 working hours per week the number of men required would be about 230. Account must also be taken of the fact than an 80,000-ton plant would require more men than the present 40,000-ton plant, and of the additional men needed to work the hydraulic presses. So that at the lowest estimate 230 to 250 men would be required for a plant of 80,000 (40,000 saleable) tons capacity. Based on 12 months’ or 360 days’ operation this means a production of less than half a ton of briquettes per man employed for an 8-hour day. Cost of labour must therefore be put at least at 20 kronor per ton of briquettes.
Maintenance and repairs, at least 3 per cent 420,000
2,000 tons lime at 50 kr. per ton 100,000
Filter cloths estimated 200,000
Other materials and miscellaneous 250,000
Administration and general expenses 250,000
Total 1,220,000
or about 30 kronor per ton of saleable briquettes. Assuming that plant cost and working capital are amortized, and amortization together with interest amounts to 14 per cent per year, this will amount to 50 kronor per ton, thus making cost of production, according to my calculation,—
Amortization and interest, about 50 kronor
Labour cost 20 “
Other costs 30 “
100 “ per tonThe cost per ton of saleable briquettes is 100 kronor assuming 50 per cent efficiency of the plant in a continuous run for one year. With briquettes of 4,500 effective calories per kilogram, this cost corresponds to a price of 155 kronor per ton for best English steam coal of 7,000 effective calories per kilogram. From this it is evident that the Dumfries method, even provided such improvements are made to obtain above- mentioned efficiency of 50 per cent, and with a continuous run of 12 months could not be economically employed when the price of coal of 7,000 effective calories per kilogram drops below 150 kronor per ton.

The above calculations are made on the assumption that the details of the process are solved, tested out and practically applied. As this however is not the case, it is my opinion that the Dumfries method should not be attempted in Sweden. Only after it has been established that the Dumfries plant, after the above-mentioned improvements, using their own fuel, can be kept in continuous operation with an efficiency of at least 50 per cent, will it be worth investigation. Then the plant should be reported on by a commission of experts on peat technique, and mechanical and heat engineering, and calculations made as to cost and operating expenses of such a plant in Sweden.


The English company, “Wet-Carbonizing Ltd.” has for a period of several years carried on experiments on a large scale at Dumfries, Scotland, and built a large plant for manufacture of carbonized peat briquettes according to the wet-carbonizing method, which plant may be considered to have been in industrial operation since the beginning of October 1919.

This was designed for a yearly production of about 60,000 tons, but not fully completed in all details; the production during the trial run at the time of my visit amounted to 130 tons of briquettes per 24-hour day, or 40,000 tons per annum.
A number of details especially the excavator, pumping system, and other mechanical arrangements were designed with great skill and appeared to function with great efficiency and regularity; while other details, e.g., the wet-carbonizing system proper, the presses, etc., did not work with satisfactory efficiency.

The finished product was obtained in the form of hard, regularly shaped briquettes of 8 per cent moisture content. These were of very good quality, and should prove an efficient fuel as a substitute for coal. One ton of briquettes equals in effective heat value 0 • 65 ton best English steam coal of 7,000 effective calories per kilogram.
Power and heat required for the plant were obtained from use of Scotch slack coal. The heat efficiency was especially unsatisfactory, as many calories being consumed in the coal as were produced in the bri­quettes. The company’s technical staff were, however, working on improve­ments on different parts of the plant by which they considered that they would be able to reach an efficiency of at least 50 per cent. This means that if carbonized peat were used for operating the plant, one-half of the peat substance could be sold as briquettes.The cost of such improved plant cannot be given with any degree of accuracy. A plant in Sweden with 50 per cent efficiency and producing 40,000 tons of saleable briquettes in 12 months may be estimated to require a capital of 12 to 15 million kronor ($3,240,000 to $4,050,000).

Under the climatic conditions prevailing in Sweden excavation of peat could hardly be continued for longer than 9 months.

Cost of production including amortization and interest for a factory to produce 40,000 tons of saleable briquettes, assuming a 50 per cent efficiency and 12 months’ continuous run, will not be less than 100 kronor per ton, corresponding to 155 kronor per ton for best English steam coal with 7,000 effective calories per kilogram.
At the present time this process should not be attempted in Sweden. Only after the plant at Dumfries has been improved, and can use its own peat fuel with a 50 per cent efficiency, should the matter be taken up and further investigated.