IE41468B1 - Process for continuous coking of peat bovey coal and wood in particle form - Google Patents

Abstract

A process for the continuous coking of peat, bovey coal, wood and the like, in particle form. Dried particles are fed into one end of a reaction chamber, stirred, and coked in the reaction chamber by heating them with hot gases, and the coked particles are removed at the other end of the reaction chamber for the purpose of cooling. The hot gases are fed in the reaction chamber over the particles to be coked in order to achieve a direct heat exchange contact between the gases and the particles. Preferably the hot gases are contacted countercurrently with the upper surface of the particle bed moving through the reaction chamber and the reaction chamber comprises a cylindrical furnace which is rotated around its longitudinal axis to stir the particles and to move them forward in the form of a bed.

Description

The present invention relates to a process for the continuous coking of peat, bovey coal, wood and tho like, in particle form, wherein dried particles are fed at one end of the reaction chamber, the particles are stirred and coked in the reaction chamber by heating them with hot gases, and the coked particles are removed for cooling at the other end of the reaction chamber.

Previously known are a great number of different processes for coking or dry-distilling organic material, mainly coal and bovey coal. The coking takes place in these processes by heating 10 the organic material in particle form with hot gases, usually hot smoke gases. These processes can thus be classified into two groups in regard to the heating with gas: processes in which the heating takes place by an indirect heat exchange contact and those in which the heating takes place by direct heat exchange contact between the hot smoke gases and the material to be coked in particle form, Thus, it is known to coke coal in a cylindrical furnace by bringing the coal in the cylindrical furnace into indirect heat exchange with the hot smoke gases fed between the cylindrical 2o furnace and the stationary mantle around it. The greatest dis- 2 41468 advantage of this process is the poor heat-transfer capacity duo to indirect heat exchange, a factor which prerequires a great difference in temperature between the hot smoke gases and the coal to he coked. In addition, the double mantle has low durability owing to the high temperature. It must also be noted that such a furnace provided with a double mantle is much more expensive than an ordinary cylindrical furnace.

Also, known are processes in which the material to be coked is fed at the upper end of the reaction shaft and is removed at its lower end, and hot gases are blown, with nozzles extending into the reaction shaft, through the material settling in the shaft. These gases effectively heat the material to be coked. These processes consume, however, a great quantity of carbon with the result that the coke yield remains relatively low, especially at high temperatures. The carbon dioxide and water vapor present in the hot gases are caused, by the good contact between the gases and the material to be coked, to react with the coke, thereby forming carbon monoxide and hydrogen gas, which naturally reduces the coke yield considerably. 2o In another similar process, oil shale is loaded into trolleys which are moved through an oblong horizontal tunnel, from the floor of which hot gases are blown upwards, and the gases flow through the trolleys and their load from below. The same disadvantages appear in this process as in the previous one.

The object of the present invention is to provide a process for the continuous coking of peat, bovey coal and wood in particle form. In the process, the heat exchange between the hot gases and the material to bo coked is good without the heating gases being in too effective a contact with the material to be coked, and consequently, the coke yield is high. The object of the invention is, in other words, to achieve a good exchange of heat between the heating gas and the solid material without allowing the heating gases to react with the solid materia].

The invention therefore provides a process for the continuous coking of peat, bovey coal and wood in particle form, wherein dried particles are fed at one end of the reaction chamber, stirred, and coked in the reaction chamber by heating them with hot gases, and the coked particles are removed at the other end of the reaction chamber for the purpose of cooling wherein the hot gases are fed in the reaction chamber over the particles to be coked in order to achieve a direct heat exchange contact between the gases and the particles.

The process according to the invention deviates from the above-mentioned processes and devices operating by direct heat exchange in the respect that therein hot smoke gases are not directed through the bed of material to be coked, but over it. Thereby the carbonization gases released from the material to be coked are able to effectively protect the solid bed from oxidation. The composition of the gas in the bed and even slightly above it is thus different from that in the furnace gas space., which has a carbon-consuming atmosphere. The carbonization gases released from the bed of solid material serve as a protective gas which prevents the oxidation of the coke.

By the process according to the invention, a high coke yield is obtained in spite of the fact that the smoke gases are brought into a direct heat exchange contact with the solidmaterial bed to be coked. The transfer of heat from the hot smoke gases into the solid material is very effective. Heat radiates from the burning gases both to tho bed of solid material and to the furnace walls, and from the furnace walls heat is transferred by conduction to the bed of solid material; this is especially effective if the furnace used is a cylindrical one in which the wall part heated by radiation and convection is transferred to a position below the bed of solid material, thereby giving heat to the material and causing the bed to rotate slightly.

The invention is described below in more detail with reference to the enclosed drawing, which depicts a schematic view of the coking of peat by the process according to the invention.

Dried peat is dry-distilled in the cylindrical furnace 4 according to the countercurrent principle. An auxiliary burner 5 is connected to the cylindrical furnace, and in this burner, flying dust, coke dust, cut peat or hot peat-coke can he burned during the entire drying process. Most of the ashes produced can be eliminated by using a suitable separate burner.

The hot smoke gases from the burner are fed at the hot end of the cylindrical furnace 4. Thereby, burning materials are released from the material to be dry-distilled and are burned by an additional air blast. The gas flow proceeds in the cylin5 drical furnace 4, giving heat to the solid material moving in the opposite direction. The heat is transferred into the material to he dry-distilled partly by the mediation of the furnace wall and partly through radiation from the hot coking gases.

In the cylindrical furnace 4 only the surface of the peat layer is in contact with the mixture of smoke gases and carbonization gases. In addition, the released carbonization gases protect the bed of solid material from oxidation. The coke yield is therefore high.

The temperature and temperature profile of a furnace 4 with direct heating can be regulated quickly and within a wide range by means of an auxiliary burner and by an additional air blast. Thus, the same unit can be used for manufacturing products suitable for different purposes. By regulating the number of revolutions and by selecting a large angle of inclination for the furnace, a high heating rate is achieved, whereby part of the produced tars crack and the coke yield increases. The previously known processes for manufacturing peat coke are not as flexible as the one according to this invention.

Thereafter, the coking-cylinder product proceeds to a cooling unit 6, wherein the temperature can be lowered by, for example, water spraying or inert gas.

The outlet' gases from the cylindrical furnace 4, which contain dust and tar, are burned in the gas burner 3· The toxic 25 phenols are eliminated from the gases simultaneously. An expensive dust and tar separation system is not necessary. The produced heat is used for the drying.

The material to be coked is dried in some suitable unit, e.g., by cylinder drying or grate drying 1. The flying dusts 30 separated in the cyclone 2 are used as fuel in the auxiliary burner of the coking furnace.

Example 1 Peat in particle form contained 1.5% ash, 71% volatiles, the analysis being C 56%, H 6%, 0 34%, N 2%. The peat was crushed 35 to a particle size less than 50 mm. The particles may be even larger (up to 100 mm), but in that case the carbonization takes a longer time. The material was dried to a moisture content of 4.3$. is advantageous to remove the moisture in a separate drying unit at least to’ a value below.20$ to reduce the heat requirement of the coking and to raise the combustion temperature of the carbonization gases.

The peat feed was 209 kg/h, which was dry-distilled according to the countercurrent principle in a cylindrical furnace 12 m long and with an inner diameter of 0.77 m. The mean delay of the material in the furnace was 2 h 34 min, the number of revolutions of the furnace being 0.5 rpm. Smoke gases at 1000°C were fed at the rate 125 Nm^/h into the furnace from a separate peat burner. Most of the heat was, however, generated by blasting 75 Nm^/h air into the hot end of the furnace, whereby part of the volatiles and stalks were burned. The temperature of the hot end was maintained at 75O°C. A suitable temperature range is 55O-1OOO°O.

The mixture of the peat-burner smoke gases and the smoke and carbonization gases produced in the furnace emerged from the colder end of the furnace at 200°C. The gases, the analysis of which was (without water): H2 6.8$·, CO 7$, CH^ 4.5$, Ng 61.4$, Ar + 02 5.3$, C02 11$, were burned after leaving the furnace.

The yield of coke was 62.8 kg/h, which is 31.5$ of the dry weight of the feed. The analysis of the coke was: ash 4.8$, volatiles 5.9$, Cfix 89.3$.

Example 2 Carbonization of wood.

Wood chips with a moisture content of 11$ were fed into the experimental apparatus described in the previous example. This time the auxiliary burner was attached to the end of the furnace and butane was burned in it at the rate of 6 kg/h. The air blast was 110 Nm'^/h, the rotational velocity of the furnace 0.7 rpm, and the corresponding delay period 2 h 10 min.

When the dry weight of the chips fed was 93 kg/h, charcoal was obtained at 26 kg/h, the temperature of the hot end of furnace being 585°C. The analysis of the charcoal was: ash 1.4$, volatiles 11.9$, 86.5$. The gases emerging from the furnace were fed into the tar separation unit.

Claims (7)

1. j.

2. A process for the continuous coking of peat, bovey coal and wood in particle form, wherein dried particles are fed at one end of the reaction chamber, stirred, and coked in the

3. A process according to Claim 1 or 2 wherein the reaction chamber used is a cylindrical furnace which is rotated around its longitudinal 15 axis to stir the particles and to move them forward in the form of a bed.

4. · A process according to one of the above claims, wherein particles to be coked have a particle size of 100 mm at the maximum, preferably less than 5θ mm. 2o 5. A process according to one of the above claims, wherein the particles to be coked have a moisture content of less than 20$ by weight.

5. Reaction chamber by heating them with hot gases, and the coked particles are removed at the other end of the reaction chamber for the purpose of cooling wherein the hot gases are fed in the reaction chamber over the particles to be coked in order to achieve a direct heat exchange contact between the gases and the particles. 10 2.' A process according to Claim 1, wherein the hot gases are contacted countercurrently with the upper surface of the particle bed moving through the reaction chamber.

6. A process according to one of the above claims, wherein the temperature of the furnace at the entrance end of the hot gases is 25 maintained at 55O-1OOO°C.

7. - A process for the continuous coking of peat, bovey coal and wood substantially as herein described with reference to the examples and the drawing.