GB2269389A

GB2269389A - Gasification of solid and liquid wastes

Info

Publication number: GB2269389A
Application number: GB9305932A
Authority: GB
Inventors: Manfred Dipl Ing Durlich; Wolfgang Dipl Chem Rabe; Olaf Dipl Ing Wehner; Hartmut Ing Findeisen; Gerd Thieme; Joachim Muller
Original assignee: LAUSITZER BRAUNKOHLE AG; Energiewerke Schwarze Pumpe AG
Current assignee: LAUSITZER BRAUNKOHLE AG; Energiewerke Schwarze Pumpe AG
Priority date: 1992-08-06
Filing date: 1993-03-22
Publication date: 1994-02-09
Anticipated expiration: 2013-03-22
Also published as: FR2694567A1; GB9305932D0; CZ385792A3; CZ281282B6; DE4226015C1; PL298422A1; GB2269389B

Description

2-269389 T ITLE Gasification PronARS This invention relates to a method

for the disposal of solid and liquid waste materials by a gasification process in fixed bed pressure gasification.

The fixed bed gasification process can be carried out with a great variety of starting materials, such as raw brown coal, brown coal briquettes, hard brown coal and pit coal. The quality of these raw materials, as regards their ash and water content, may fluctuate within wide limits. The expenditure involved in processing the gasification material is moderate. These relatively limited demands made by the fixed bed pressure gasification process on the gasification material and the possibility of utilising the products as such have led to the use of waste materials for the purpose.

A fundamental disadvantage of fixed bed pressure gasification is that the crude gas contains dust and hydrocarbons of high and low boiling point as well as organic and inorganic compounds which are soluble in water and necessitate costly auxiliary plant for the extraction and utilisation of individual products and also for the prevention of hazards to the environment.

C1 DD 259 875 proposes a system in which, in order to avoid waste products, the bulk height of the fuel in the fixed bed pressure gasifier is lowered considerably, so that by the resulting temperatures of about 10000C in the gas container the tars, oils and gas particles will be converted in the said container into crude gas. This process cannot be properly controlled from the standpoint of operating safety, as the extremely low solid bed leads to irruptions of oxygen liable to cause explosions in apparatus subsequently used. In a further system, proposed in DD 43253, the liquid and solid constituents contained in the gas are to be converted into gas autooxidatively, gasification agents being fed into them after leaving the gas generator. This method is not economically rational, since some of the gas generated undergoes combustion. The performance of this process does not guarantee any defined conversion of the liquid and solid constituents. Since, moreover, the proposal incorporates no definite teaching which can be carried out in practice, the method described must be regarded as liable to involve gas explosions.

DE 150475 describes a solution in which, in regasification of crude gas from fixed bed pressure gasification, higher carbons are to be converted by hydro-cracking, with the use of hydrogenation catalyst.

This process suffers from the drawback that the temperature at which the crude gas enters the regasifier has to be adjusted to the working temperature of the catalyst. When brown coal is used in the gasification process this object can only be achieved by recourse to complicated control methods and process engineering. A further drawback of the process resides in the rapid contamination of the catalyst with coal dust and particles of ash carried along with the crude gas in addition to the resulting high operating costs. DE 253 2197 and 253 2198 also describe proposals for the regasification of hydrocarbons from the crude gas of fixed bed pressure gasification by introducing the said crude gas, while adding oxygen, into a regasifier containing a solid bed of inert or catalyst material, causing gasification reactions and cracking reactions to occur as a result of temperature increases.

This method is disadvantageous inasmuch as neither the composition of the crude gas nor the quantity thereof in the regasifier can be controlled and the fixed bed in the regasifier, owing to contamination from the ingress of dust and ash, may cause a reduction in performance or the cessation of the gasification process.

For waste materials containing organic noxious substances such as dioxins and furans as well as for those containing heavy metals, solutions are proposed in which residues containing heavy metals are converted, by binding them into argillaceous materials (DE 391825 9, 3713482, 3919011 or 3502215) forming solid disposable products which can then be placed in underground waste disposal dumps, in some cases at considerable cost.

Alternative proposals are based on fusion solutions. Examples of the latter are described in DE 3939344 and 3206984. These installations call for a very high consumption of energy. Most of them are at present at the laboratory and pilot plant stage, and considerable development work and expenditure of time will be required before they can be put into practice.

In the sphere of gasification a proposal is known from DE 267880 whereby a liquid fuel containing ash is conveyed separately and independently of a burner supplied with a pulverulent fuel, together with steam through a feed pipe to the reaction chamber, while the oxygen required for the autothermal partial oxidation of the liquid fuel with an ash content is fed to the gasification reactor via the coal dust burner.

In this process the gasification of liquid residues calls for the consumption of large quantities of coal dust, the use of which leads to high gas production costs. This method sets strict limits to the quantity of liquid residues that can be used.

Further processes are known in the sphere of fixed bed pressure gasification and reference is made to DE 2619302, 3342383 and 3327203, proposing slag is drawn off in liquid form as a means of melting down inorganic noxious substances, but such methods fail to solve the problem of ensuring that no heavy metal vapours are absorbed into the crude gas.

One object of this invention is to enable the processes for the disposal of solid and liquid waste materials to be further developed in such a way as to improve, with a high degree of efficiency, the elimination of inorganic toxic substances or even organic toxic substances having a high boiling point.

According to this invention there is provided a process for the disposal of solid and liquid waste materials by a gasification process using fixed bed pressure gasification, in which process the fixed bed pressure gasifier is fed with 1 to 80% of waste and 20 to 99% of the gasification material as lump brown coal, the proportion of lignite being adjusted in such a way that the calorific value of the gasification material is at least 12 MJ/kg, the heavy metal constituents of the waste with a boiling point above 6500C amounting with respect to the coal proportion to below 5g/kg, the grain size of 6 the gasification mixture below 10 mm being not more than 20% and the, proportion of waste components with a bulk density below 400 kg/m3 not amounting to over 50% of the gasification material.

Thus this invention solves the problem by feeding a fixed bed pressure gasifier with 1 to 80% waste and 20 to 99% lump brown coal simultaneously.

The proportion of brown coal fed in is adapted to the noxious constituents and also to the calorific value of the waste materials.

The said supply of brown coal is set in proportion to the salt, heavy metal, dioxin and furan content and in inverse proportion to the calorific value of the waste materials. In the fixed bed pressure gasifier the brown coal, by the formation of a defined temperature profile in the pile, is converted, at 300 to 800 OC and with a time dwell of >1h, into an active material with a specific surface area of about 400m2/g, which absorbs the vapours of heavy metal, salt, dioxin and furan emanating together with the gasification gas from the waste materials and conveys them into deeper zones of the pile with temperatures of about 12001C. At these temperatures the organic toxic compounds are destroyed and the inorganic compounds mainly bound into the slag occurring.

In the case of a fixed bed pressure gasifier the operation of selecting the aforementioned temperature profile, the maximum temperature in the pile and the time of dwell required for the brown coal at temperatures of 300 to 8000C for the formation of active substance is carried out as follows:the time of dwell of > 1 h for the brown coal in a temperature range of 300 to 8000C is obtained by setting the oxygen loading to about 3400m3 02/h. If it is less, the time of dwell required is thereby lengthened; the maximum temperature in the pile is set by selecting a suitable steam-to-oxygen ratio. If it is set at 7 kg steam/lm.3 i.N.0, the maximum temperature is about 12000C. The adoption of a lower ratio increases the maximum temperature accordingly; the position and the formation of the reaction zones, evident from the temperature profile of the zone temperature measurements or the periphery of the fixed bed gasifier in one or more planes are kept at the required level by a continuous discharge of slag, taking into account the ratio of the quantity of mineral fed in to the quantity of slag discharged. if this is set correctly the average temperature on a level with the top of the rotating grid is about 3500C, while at the level 2m higher up it is about 4500C. The maximum temperature, however, should always be close to the melting point of the ash. A grain size analysis of the discharged slag confirms that the optimum maximum temperature is obtained when the proportion of grains of less than 5mm in size does not exceed 40%.

Further control parameters which can be used for the position and formation of the reaction zones are the C02 content of the gasification gas, which should be < 40% by volume, the outlet temperature of the crude gas, which should be between 350 and 5500C, the temperature of the slag, which should be between 250 and 3500C, and the differential pressure of the generator pile, which must not rise to above 10 kPa.

Optimum operation is achievable by a combination of all the parameters given.

The fixed bed pressure gasifier is fed via a sluice with the solid waste mixed with coal. If it is in a compact form the grain size should be between 5 and 10Omm, the bulk density not being allowed to fall below 500 kg/m3.

9 Liquid waste with 1 to 40% of slid content is introduced directly into the pile through the top central part of -Ehe fixed bed pressure gasifier and constitutes 1 to 20% of the gasification material used.

Waste substances which can be thus processed include light-weight shredder material, plastic waste, textile waste, car tyre shreds, paper and wood waste, charged active coke, contaminated earth, sewage sludge and paint sludge as well as oil and tar mixtures with a solid content.

The slag is continuously removed from the fixed bed pressure gasifier by means of a rotating grid via a sluice. The slag contains no contaminants harmful to the environment. It can be used in the building industry or dumped.

The crude gas leaving the fixed bed pressure gasifier still contains harmful constituents which by reason of their low boiling point could not be conveyed into lower zones of the pile which are at a higher temperature and destroyed or rendered harmless. Disposal of this gas is effected in plant for the preparation of gas or gas condensates and/or in flue current gasification plant.

The particular advantage of the process resides in the fact that toxic vapours are absorbed by the active material generated from the coal in the fixed bed pressure gasifier and conveyed into zones which are at a higher temperature and in which they can be rendered harmless, as well as the fact that an active substance which can be used for the aforementioned purposes is produced in the same reactor in which the disposal of the waste is effected.

An embodiment by way of example for the performance of the invention is illustrated by the drawing and described in detail in the following.

A fixed bed pressure gasifier 1, operated at a pressure of 25 bar, is fed with waste at an approximate rate of 10.5 t per hour.

The constituents of the waste are summarised in the following table:

Heavy Metals Calorific Value Grain Size Bulk density Boiling point lomm 400 kg/m 650 0 c Proportion Flow Density Flow rate mg/kg g/h MJ/kg MJ/hxl03 rate j % t/h Kg/m t/h (2) 3 t/h contaminated 8570 25710 1.5 4.5 70 2.1 1200 earth (3) 2 t/h light-weight shredder 730 1460 6.3 12.6 5 0.1 200 2 material (4) 2 t/h contaminated 300 600 8.0 16.o 5 0.1 300 2 (5) 0.5 t/h car tyre shreds 21000 10500 28.0 14.0 2 0.01 350 0.5 (6) 2 t/h sewage sludge 1275 2550 4.0 8.0 10 0.2 450 (40% TS) (7) 1 t/h solid mixture of tar & oil 10 10 25.1 25.1 20 0.2 1000 10.5 t/h waste 40 830 g/h 80.2x103 W/h 2.71 t/h 4.5 t/h The coal requirement is determined in accordance with the preselected limit values, such as heavy metal content in relation to proportion of coal to be < 5g/kg, calorific value > 12 MJ/kg of gasification material, constituents of waste of a bulk density of < 400 kg/m3 to be < 50%, and overall bulk density > 500 kg/m3 in the gasification material.

In the example given, with a quantitative heavy metal flow rate of 40830 g/h, the coal requirement (40.830 g/h heavy metal; 5g heavy metal/kg of brown coal) amounts to 8.166 t/h. With this proportion of coal the further limit values (calorific value, grain size < 10 mm and bulk density < 400 kg/m3) are all maintained. No alternation to the constituents is required. The hourly quantity of gasification material fed to the fixed bed pressure gasifier 1 thus amounts to 10.5 t waste 4 + 8.166 t brown coal 8 = 18.666 t. The quantity of oxygen required for the gasification amounts to 0.0083 J i.N. 02/MJ heat content of the gasification material. It follows that the quantity of oxygen will be: (80.2 X 103 MJ/h + 16.8 X 103MJ/H x 8.166 t/h) x 0.0083 M3 i. N. /MJ = 18 0 0 j i. N1h The time of dwell required with this setting in order to activate the brown coal is calculated as f ollows:

Bulk vol. of reactor x proportions between 300 and 5000C Gasification material flow rate/bulk density of gasification material 80M3 x 0.7 3 2.1h 18.666 kg/h/700 kg/m.

At 2.1h the activation time is adequate.

The quantity of oxygen 10 mixed with 12.6 t of steam per hour, is introduced into the fixed bed gasifier via the rotating grid 9. The steam-to-oxygen ratio thus selected, i.e. 7 kg steam/m3 i.N. 0,, results in a temperature of 12000C in the oxidation zone of the fixed bed gasifier. A slag granulate 12 occurs the heavy metals being melted into it, in a quantity of gas of 4t/h, and is continuously sluiced out via the rotating grid, with due observance of the required ratio of the quantity of mineral material fed in to the quantity of slag discharged (ratios 1.2:1), the said granulate then being put to use. The zone levels decisive for the formation of active material are monitored by the temperature measurements 11 of the periphery of the reactor.

In the fixed bed pressure gasifier the hydrocarbons contained in the contaminated earth are distilled off. The old tyre material and lightweight shredder material are converted to the extent of 40 to 70% into gas constituents and 20 to 50% into hydrocarbons. 3 to 12% 14 according to the composition passes into the ash/slag fraction. The residues are discharged as an ash/slag mixture through the rotating grid.

Via the crude gas receiver 13, 12,600 m3 i.N. of dry crude gas and 8400 J i.N. of steam/h are conveyed at a temperature of about 4500C via the crude gas manifold 14 into apparatus for the preparation of gas or gas condensate and/or into flue current gasification plant. The composition of the crude gas thus introduced is as follows:

C02 33.5% CO 15.0% H2 36.0% CH4 12.5% Nn 0.9% 02 0.1% cl-C4 2.0% The crude gas also contains about 90g of cyclic and aliphatic hydrocarbons/M3 i.N. and 10g of dust/m3 i.N., which has an ash content of about 20%.

In the drawing the reference numerals identify the following parts.

1. Fixed bed pressure gasifier 2. Contaminated earth 3. Light-weight shredder material 4. Contaminated wood waste 5. Car tyre shreds 6. Sewage shreds 7. Mixture of tar, oil and solids 8. Brown coal 9. Rotating grid 10. Mixture of gasification media 11. Temperature probes 12. Slag granulates 13. Crude gas receiver 14. Crude gas manifold.

r 16

Claims

1. Process for the disposal of solid and liquid waste materials by a gasification process using fixed bed pressure gasification, in which process the fixed bed pressure gasifier is fed with 1 to 80% of waste and 20 to 99% of the gasification material as lump brown coal, the proportion of lignite being adjusted in such a way that the calorific value of the gasification material is at least 12 MJ/kg, the heavy metal constituents of the waste with a boiling point above 6500C amounting with respect to the coal proportion to below 5g/kg, the grain size of the gasification mixture below 10 mm being not more than 20% and the proportion of waste components with a bulk density below 400 kg/M3 not amounting to over 50% of the gasification material.

2. Process according to Claim 1, wherein the liquid waste contains 1 to 40% of solid material and is fed direct to the fixed bed gasifier in a proportion of 1 to 20% of the gasification material used.

3. Process according to Claim 1 or 2, wherein the fixed bed gasifier is fed with the solid waste in a lumpy compacted form with a grain size of > 5 and < 10Omm and mixed with coal.

4. Process according to Claim 1 or 2 or 3, wherein the fixed bed gasifier can be fed simultaneously with different waste materials mixed in proportion which depend on the degree to which noxious substances are present and on the density as well as on the grain size range of the said waste materials.

5. Process according to Claims 1 to 4, wherein the fixed bed gasifier process is controlled in such a way that the temperature profile and also the time of dwell of the gasification material and the formation of the zones in the fixed bed pressure gasifier lead to an activated coal which absorbs noxious substances (mainly PCB and/or dioxin as well as heavy metals and/or salt vapours), which are conveyed into zones of the fixed bed pressure gasifier with temperatures of > 12001C, in which organic noxious substances are destroyed or melted into the slag particles.

6. Process according to Claim 5, wherein the time of dwell required in the activation temperature zone in order to form active substances is set by means of the quantity of oxygen supplied per hour.

7. Process according to Claim 5, wherein the melting point of the noxious substance is set by means of the ratio between vapour and oxygen and monitored by the granular structure of the slag.

8. Process according to any one of Claims 5 to 7, wherein the position and formation of the reaction zones are kept at the necessary level by continuous discharge of the slag through a rotary grate, observing the required ratio between the quantityof mineral introduced and the quantity of slag discharged and are monitored at intervals by a number of temperature measurements.

9. Process according to Claim 8, wherein the temperature measurements are carried out at two levels evenly distributed around the periphery of the reactor.

10. Process according to any one of Claims 1 to 6, wherein the process is combined with plant for the preparation of gas and condensate and/or with flue current gasification apparatus.

11. Process for the disposal of solid and liquid waste materials substantially as described herein and exemplified with reference to the drawings.