FR2567143A1 - Process and fluidised bed apparatus for the hydrolysis, gasification and combustion of low-grade fuels - Google Patents

Abstract

Energy is produced from a low-grade fuel, for example a bituminous schist, in three separate stages, namely: 1. pyrolysis and gasification of the organic substances in air; 2. combustion of the residual carbon in solid form with the aid of air, and 3. combustion of the gases and vaporised liquids originating from the first stage and of the gases and carbon monoxide originating from the second stage, the first two operations being performed in a fluidised bed. The invention finds its main application in the production of energy, of steam or of electricity by the use of cheap raw materials.

Description

 The invention relates to a method, a technique and equipment for the treatment of solid fuels in power plants, chemical plants and cement plants, for the production of energy, steam, electricity or petrochemicals. The technique according to the invention relates particularly to fluidized bed fuels and fine-grained solid fuels.

 The invention particularly relates to oil shales having a low organic content (7-35%), a high carbonate content (20-70%) and a high sulfur content (0.5-4%). Almost all of the organic material is removed, the energy loss caused by the decomposition of the carbonates is low, and the sulfur is removed in a separate stream, leaving only the residual ash and the flue gases noncontaminated. The efficiency is high, and the high temperature combustion of effluent gases is comparable to that found in high-pressure boilers and the most modern power plants.

 The method and apparatus according to the invention derive from research and development work carried out at the Hebrew University of Jerusalem under contracts with the Israeli Ministry of Energy and Infrastructure. The Israeli Ministry of Energy and Infrastructure has an irrevocable and nonexclusive license to practice and practice the process and apparatus of the invention, and has in particular the right to grant sublicences to third parties for the purpose of implementing the method and apparatus according to the invention for any application.

Many low-quality bituminous shales contain only 7-20% organic substances and large amounts of carbonates (40-70%). When these oil shales are treated at a temperature greater than 7008000C, an endothermic reaction of carbonate decomposition occurs.
CaCO3 + CaO + C02
Heat of reaction: 1.76 MJ / kg CaCO3
(420 kcal / kg)
4.04 rAJ / kg C02
(965 kcal / kg)
The combustion of these oil shales above 8000C reduces their already low heat of combustion by 20-40%, by reducing it from 3.35-5.02 MJ / kg (800-1200 kcal / kg) to 2, 51-3.77 MJ / kg (600-900 kcal / kg).

 In addition, the decomposition of carbonates further weakens the ash, and the mechanical manipulation and abrasion cause their collapse, with dust formation. These move to the boiler and erode the boiler piping; they also arrive at the chimney and cause a pollution of the atmosphere.

Existing fluidized bed processes, which rely on the pyrolysis, gasification and oxidation of residual coal from fine-grained, dilute solid fuels, involve direct combustion. See for example Rorbach,
United Nations Symposium on the Development and Use of Oil Shale Resources, Tallim, USSR, 26 August-4 September 1968. The Tami process, currently under development by Israel Chemicals Ltd., is an analogous process.

 In the German process, fine-grained bituminous shale is introduced into a fluidized bed. Primary air is sent to the bottom of the fluidized bed combustion chamber, the secondary air being injected into the upper layers of the fluidized bed. Some of the boiler tubes are placed directly in the fluidized bed and others inside the boiler to which the hot combustion gases and fine dust flow.

 In the fluidized bed, pyrolysis, gasification, oxidation of the volatile gases and carbon, and finally decomposition of the carbonates were simultaneously carried out at a bed temperature of 800-100 ° C.

This process of direct combustion of oil shale has the following drawbacks: a large part of the heat produced is used to decompose the carbonates and heat the ashes to a high temperature, which reduces the efficiency of the production of electrical energy, as well as the combustion temperature. The decomposition of carbonates weakens the ashes, which collapse by forming dust. These dusts move to the steam generator, where they cause erosion of the tubes. They also arrive at the chimney and contribute to air pollution. For combustion carried out at 800-10000C, most of the sulfur reacts with the mineral ash, which forms sulphates which render the ashes unusable for other applications, for example the preparation of Portland cement. Discharges of discharge are presented
Experience has shown that there is a strong reduction in carbonate decomposition if pyrolysis, gasification and residual carbon oxidation occurred at 400-7000C. The process according to the invention allows these operations to take place in a fluidized bed at a lower temperature, which limits the decomposition of carbonates.

 If pyrolysis and gasification are carried out in a fluidized bed at 350-7000C, it is found that the pyrolysis time is very short (one to four seconds), that the time required for the heating of oil shale grains is 2- 20 seconds according to their particle size, and that the pyrolysis reaction proceeds almost uniformly in the particle mass; moreover, it is a first-order reaction. Fifty to ninety percent of the organic matter is converted into organic gas and tar.

 When the pyrolyzed particles are burned in air in a fluidized bed at 350-7000C, residual carbon oxidation takes place according to the core shrinkage model, that is to say that it is the diffusion oxygen through the outer ash layer which is the mechanism defining the reaction. The rate of oxidation increases with the concentration of oxygen. Almost all carbon is converted to carbon monoxide and carbon dioxide.

 Organic gas effluents, entrained or vaporized tar, as well as carbon monoxide can burn in excess oxygen or secondary air at very high temperatures (800-18000C) to produce energy, steam or electricity. They can also be processed to obtain petrochemicals. Due to an appropriate design of the fluidized beds and a good regulation of the particle size distribution of the filler particles, these gases can be completely removed from the entrained solids. Alternatively, if the sulfur is to be removed in solid form, a certain amount of fines can be left to allow desulfurization of the gases at the high gas combustion temperatures.

 Ashes from the fluidized combustion bed are sulfur-free and can be used as a filler for a cement plant or a unit for manufacturing other building materials. It is not necessary to dump the ashes on an embankment and treat them with water. Thus, the entire oil shale charge can be used, while still decreasing the water demand.

 The invention will be better understood with reference to the description below and the attached drawings, which show embodiments of the invention.

 Figure 1 is a schematic representation of a first embodiment of the invention for using fine-grain solid fuels in a fluidized bed. In this embodiment, the three basic operations are carried out in separate stages (I) pyrolysis and gasification of the solid organic materials, (II) combustion of residual carbon in the solid effluent of the first stage, and (III) ) combustion of the organic gases and entrained or vaporized tar from the first stage, as well as carbon monoxide from the first stage at high temperature, providing a source of energy.

 The fine-grained solid fuel is introduced into the compartment (1). The effluent gases (2) of compartment II are introduced at the bottom of compartment I.

Pyrolysis (3) and gasification (4) are carried out at 3507000C in the fluidized bed.

 The spent pyrolysed schist from compartment I flows (5) into compartment II. Air (6) is sent to the bottom of compartment II. The oxidation of residual carbon (8) and the heating of the air and the cooling of the ashes (7) are carried out in the fluidized bed of compartment II at 350-7000C. The used ashes (9) are extracted from compartment II.The ashes are designated A.

The gas (11) from the compartment I is, as far as necessary, mixed with secondary air (10) in a mixed gas burner (12), and it burns in the compartment
III at 800-18000C. The walls of compartment III may be lined with tubes for heat transfer and thus transformed into a radiation section of the boiler. The effluent combustion gases (13) arrive at the boiler or at the convection portion thereof.

Alternatively, compartment III can be eliminated, in which case the effluent cases (11) from the compartment
I can be processed to give petrochemical products.

 The fines are continuously extracted from the fluidized bed and enter compartment III. At the high combustion temperature prevailing in compartment III, the two decomposition reactions of carbonates and the combination of gaseous sulfur dioxide with calcium oxide are simultaneously carried out. In this way, the sulfur is removed upstream of the chimney, which avoids air pollution by sulfur.

Simultaneously, ash desulphurisation (9) takes place in both fluidized beds at 350-7000C. For example, high sulfur shale can be used as a feedstock in this process, and used ash can be used as raw material for cement production.
Portland or other building materials.

 Figure 2 is a schematic representation of a second embodiment of the invention. The three fundamental operations studied above are found in the three distinct stages of embodiment number two. However, the solid fuel and the gases flow countercurrently in the first embodiment, whereas in this second embodiment, the feed gas (usually air) is divided into two streams, which flow in parallel in both compartments.

 A finely divided solid fuel (1) is introduced into compartment I of the process. Air or another gas (2) is introduced at the bottom of compartment I. Pyrolysis (3) and gasification (4) take place in the fluidized bed at 350-7000C.

 Pyrolysed spent shale (5) enters compartment II through one or more openings in the vertical partition between compartments I and II.

 Air (6) is introduced at the bottom of compartment II.

The residual carbon oxidation (8) and the air heating and ash cooling (7) take place in the fluidized bed in compartment II at 350-700 C. The used ash (9) is extracted from the compartment II.

 The gas (11) from compartment I is mixed with the gas (10) from compartment II (and / or if necessary with secondary air) in a mixed gas burner (12) and then burns in compartment III at 800-18000C. The walls of compartment III may be lined with tubes for heat transfer, and thus transformed into a radiation section of the boiler. The effluent combustion gas (13) arrives at the boiler or at the convection portion thereof.

 Alternatively, compartment III may be removed, in which case the effluent gases (11) and / or (10) from compartments I and II, respectively, may be processed for processing into chemicals or other products.

The fines are continuously extracted from the two fluidized beds and enter compartment III. As in the first embodiment, the sulfur is removed upstream of the chimney, which eliminates air pollution by sulfur. Likewise, the ashes (9) are desulphurized and can be used as raw material for the production of Portland cement or other building materials
As an example, let's take a representative Israeli oil shale with the following composition
C 10.07% C 2 (mineral) 24.6
H 1,19 Ashes 57,2
N 0.32 Water 2.9
S 1.38 PCI 4.46 MJ / kg
(1066 kcal / kg)
0 2.34
If the pyrolysis and gasification are carried out at moderate temperatures with heated air, a combustible gas containing 50 g of tar per cubic meter is obtained. The
PCI of this gas, including tar, is 6.40 MJ / m3 (1530 kcal / m3).

 Pyrolyzed spent shale contains 1.1% carbon, and it can be oxidized and cooled in air. After oxidation, spent shale or ashes contain only 0.3% carbon and 0.1% sulfur. The decomposition rate of carbonates is 20% or less.

When burning the effluent gas from the compartment
With the residual oxygen in the gas from compartment II, a temperature of 175 ° C. is reached in a combustion chamber using ordinary gas. The overall yield of the use of Israeli oil shale is, in the context of the process according to the invention, 86%.

RESIDUAL PRODUCT OF CONCENTRATE OF SUB-BITUMINOUS CHARCOAL (Roche)
THERMAL BALANCE

Quantity <SEP> MJ / <SEP> kcal / <SEP> Heat <SEP>%
<tb> kg <SEP> m3 <SEP> unit <SEP> unit <SEP> MJ <SEP> kcal
<tb> Entry
<tb> 1. <SEP> Roche, <SEP> PCI <SEP> 1 <SEP> - <SEP> 5.72 <SE> 1367 <SEP> 5.72 <SE> 1367 <SEP> 100
<tb> 2. <SEP> Air <SEP> preheated <SEP> to <SEP> 300 C <SEP> - <SEP> 0.578 <SEP> 0.40 <SEP> 94.4 <SEP> 0.23 <SEP > 54.5 <SEP> 4.0
<tb> 5.95 <SEP> 1421.6 <SEP> 104.0
<tb> Exit
<tb> 1.Heat <SEP> of the <SEP> gas <SEP> of <SEP> combustion
<tb> (1600C) <SEP> 1.8 <SEP> 2.63 <SEP> 628.8 <SEP> 4.74 <SEP> 1131.9 <SEP> 82.8
<tb> 2. <SEP><SEP> Heat <SEP> Ash <SEP> to <SEP> 855 C <SEP> 0.7556 <SEP> 1.00 <SEP> 239.4 <SEP> 0.76 <SEP> 180.9 <SEP> 13.2
<tb> 3. <SEP> Ash <SEP> PCI <SEP> 0.7556 <SEP> 0.31 <SEP> 73 <SEP> 0.30 <SEP> 72.7 <SEP> 5.3
<tb> 4. <SEP><SEP> losses of <SEP> heat <SEP> 0.15 <SEP> 36.1 <SEP> 2.7
<tb> 5.95 <SEP> 1421.6 <SEP> 104.0
<tb> BITUMINOUS SHALE - THERMAL BALANCE

Quantity <SEP> MJ / <SEP> kcal / <SEP> Heat <SEP>%
<tb> kg <SEP> m3 <SEP> unit <SEP> unit <SEP> MJ <SEP> kcal
<tb> Entry
<tb> 1. <SEP> Shale <SEP> bituminous <SEP> PCI <SEP> 1 <SEP> - <SEP> 4.46 <SEP> 1066 <SEP> 4.46 <SEP> 1066 <SEP> 100
<tb> 2. <SEP> Air <SEP> to <SEP> 300 C <SEP> - <SEP> 0.327 <SEP> 0.40 <SEP> 94.4 <SEP> 0.13 <SEP> 30.9 <SEP> 2.9
<tb> 4.59 <SEP> 1096.9 <SEP> 102.9
<tb> Exit
<tb> 1. <SEP> Gases <SEP> from <SEP> combustion <SEP> to <SEP> 1750 C <SEP> - <SEP> 1,133 <SEP> - <SEP> - <SEP> 4.00 <SEP > 957.6 <SEP> 89.8
<tb> 2. <SEP> Used shale <SEP>, <SEP> PCI <SEP> 0.785 <SEP> - <SEP> 0.14 <SEP> 33.5 <SEP> 0.11 <SEP> 26.3 <SEP> 2.5
<tb> 3. <SEP> Heat <SEP> of the <SEP> shale <SEP> used,
<tb> to <SEP> 378 C <SEP> 0.785 <SEP> - <SEP> 0.40 <SEP> 94.5 <SEP> 0.31 <SE> 74.4 <SEP> 7.0
<tb> 4. <SEP><SEP> Decomposition of <SEP> Carbonates <SEP> 0.036 <SEP> - <SEP> 4.04 <SEP> 965 <SEP> 0.15 <SEP> 34.7 <SEP> 3.2
<tb> 5. <SEP> Losses <SEP> of <SEP> heat <SEP> 0.02 <SEP> 3.9 <SEP> 0.4
<tb> 4.59 <SEP> 1096.9 <SEP> 102.9
<tb> Asphaltic sand - Thermal balance

Quantity <SEP> MJ / <SEP> kcal / <SEP> Heat <SEP>%
<tb> kg <SEP> m3 <SEP> unit <SEP> unit <SEP> MJ <SEP> kcal
<tb> Entry
<tb> 1. <SEP> Sand <SEP> Asphaltic <SEP> PCI <SEP> 1 <SEP> - <SEP> 3.60 <SEP> 861 <SEP> 3.60 <SEP> 861 <SEP> 100
<tb> 2. <SEP> Air <SEP> preheated <SEP> to <SEP> 300 C <SEP> - <SEP> 0.109 <SEP> 0.40 <SEP> 94.4 <SEP> 0.05 <SEP > 10.3 <SEP> 1.2
<tb> 3.65 <SEP> 871.3 <SEP> 101.2
<tb> Exit
<tb> 1. <SEP><SEP> Heat of the <SEP> gas <SEP> of
<tb> combustion <SEP> (1980 C) <SEP> - <SEP> 0.876 <SEP> 3.30 <SEP> 787.7 <SEP> 2.89 <SEP> 690 <SEP> 80.01
<tb> 2. <SEP> Heat <SEP> of <SEP> ash <SEP> to
<tb> 600 C <SEP> 0.905 <SEP> - <SEP> 0.63 <SEP> 150 <SEP> 0.57 <SEP> 135 <SEP> 15.7
<tb> 3. <SEP> Ash, <SEP> PCI <SEP> 0.905 <SEP> - <SEP> 0.20 <SEP> 48.6 <SEP> 0.18 <SEP> 44 <SEP> 5.1
<tb> 4. <SEP> Losses <SEP> of <SEP> heat <SEP> - <SEP> - <SEP> - <SEP> - <SEP> 0,01 <SEP> 2,3 <SEP> 0, 3
<tb> 3.65 <SEP> 871.3 <SEP> 101.2
<Tb>

Claims (15)

claims  A process for the production of pyrolysates from solid fuel sources having a high content of pyrolysable constituents, characterized in that it consists in (a) pyrolyzing and gasifying solid organic substances in an air stream or a other suitable gaseous medium in a fluidized bed; (b) burning the residual carbon of the solid residue of stage (a) in a fluidized bed; (c) directly using and / or recovering vapourized gases and liquids and tars from stage (a), as well as carbon monoxide and other gaseous products from stage (b).  2. Method according to claim 1, characterized in that the solid fuel source has a low organic content and a high content of sulfur and carbonates.  3. Method according to claim 1, characterized in that the solid fuel source has a low content of organic substances and a high content of sulfur and carbonates, or is an asphaltic sand.  4. Method according to any one of claims 2 or 3, characterized in that fines from the solid fuel are added to the main charge, these fines being entrained in the pyrolysis gas flowing overhead to react on gases containing sulfur to form calcium sulphate, which is separated.  5. Method according to any one of claims 2 or 3, characterized in that lime fines or carbonates are added to the main raw material charge, to flow overhead with gaseous pyrolysis products and react in the gas combustion chamber with gaseous products containing sulfur to form calcium sulphate, which is removed from the gaseous effluents.  6. Method according to any one of claims 1 to 3, characterized in that chemicals are extracted from the stage (a).  7. Method according to any one of claims 1 to 6, characterized in that the pyrolysis is carried out in stage (a) at 350-7000C.  8. Process according to any one of claims 1 to 7, characterized in that the gases and vapors of the two stages are burned with the use of heat.  9. Process according to any one of claims 1, 2 or 4 to 8, characterized in that the fuel source is a low-quality bituminous shale having an organic substance content of about 7 to 35% by weight. sulfur content of about 0.5 to 4% by weight and a carbonate content of about 2-70% by weight.  A process for producing pyrolysates from solid fuel sources having a high content of pyrolyzable components, characterized in that it is carried out in several stages, essentially as described above.  11. Apparatus for carrying out a process for the use of a low quality fuel according to claim 1, characterized in that it comprises a fluidized bed for pyrolysis and gasification, packed with a means for introducing a solid fuel therein, means for moving the spent shale from this compartment (a) to another compartment (b), which compartment (b) is placed below the compartment (a) and containing a fluidized bed, a means for introducing air into the bottom of (b), and a means for extracting spent ash from the bottom of (b), a means being further provided to burn the effluent gases and vaporized products of (a) and the gaseous products of (b).  Apparatus according to claim 119, characterized in that a third stage (c) is provided in which the products of stages (a) and (b) are burned, if necessary in the presence of additional air.  13. Apparatus according to claim 12, characterized in that the compartment of the stage (c) is placed above the compartment of the stage (a).  Apparatus for the use of a low quality fuel by a process according to claim 1, characterized in that it comprises a fluidized bed compartment for pyrolysis and gasification of the solid fuel in the form of particulates. fine particle size, comprising a means for introducing the solid fuel, an overflow means for the gasified products, a means for introducing air or other suitable gaseous fluids into the bottom of the compartment, and another compartment (b) which is arranged contiguously with the compartment (a), means being provided for introducing the spent pyrolytically treated slate from the bottom of (a) to the bottom of (b), the compartment (b) containing a fluidized bed, a means being provided for introducing air in the vicinity of the bottom of (b), another means being provided for extracting the ashes from the bottom of (b), with an outlet for the gaseous combustion products at the head of the compartment in which this s products come into contact with the products of (a).  15. Apparatus according to claim 14, characterized in that there is provided above the compartments (a) and (b) another compartment (c) in which the gaseous products of (a) and (b) burn to give a usable energy.