EP0948583A1

EP0948583A1 - Method of gasifying solid fuels in a circulating fluidized bed

Info

Publication number: EP0948583A1
Application number: EP97952838A
Authority: EP
Inventors: Johannes Albrecht; Johannes Loeffler
Original assignee: Metallgesellschaft AG
Current assignee: MG Technologies AG
Priority date: 1996-12-18
Filing date: 1997-12-01
Publication date: 1999-10-13
Anticipated expiration: 2017-12-01
Also published as: AU5657598A; JP2001506288A; AU722068B2; BR9714421A; DE59702967D1; ES2155270T3; DE19652770A1; EP0948583B1; WO1998027182A1; CA2275646A1

Abstract

Combustible fuels, for example waste substances, biomass or coal, are gasified in a circulating fluidized bed with the addition of oxygenous gas at temperatures ranging from 700 to 1000 °C. A fuel gas is obtained which contains dust and hydrocarbons, including higher hydrocarbons (C6+ hydrocarbons), and has a calorific value of between 2000 and 8000 kJ/m3. The dust-laden gas is passed through a separation chamber in which the higher hydrocarbons present in the gas are largely separated by the addition of gaseous oxygen at temperatures ranging from 800 to 1200 °C and below the temperature of the ash melting point. The content of C¿6+ ?hydrocarbons present in the gas emerging from the separation chamber is at most 10 wt % of the initial content. The gas from the separation chamber is cooled and dedusted and passed through at least one bed or at least one reactor with granular solids which bind with pollutants. The gas-purification process is carried out without forming waste water.

Description

Process for gasifying solid fuel in the circulating

fluidized bed

description

The invention relates to a process for gasifying solid fuels in the circulating fluidized bed, the fuels being gasified in a gasification reactor with the supply of oxygen-containing gas at temperatures in the range from 700 to 1000.degree. C., a gas-solid mixture from the upper area of the gasification reactor Separator feeds, from the separator dust and hydrocarbons including higher hydrocarbons with more than 6 carbon atoms in the molecule (C ^ hydrocarbons) containing gas with a calorific value of 2000 to 8000 kJ / m ³ and separately separated solids and the solids at least partially leads back into the lower region of the gasification reactor. Methods of this type are known from DE-A-42 35 412 (corresponding to US-A-5 425 317) and DE-A-44 12 004. In the known processes, the gas coming from the separator and containing combustible components is gasified or burned to form liquid slag, and the liquid slag is removed from the process. The gas generated during combustion or gasification is cleaned in contact with the washing liquid. It becomes necessary to prepare or dispose of the used washing liquid.

The invention has for its object to modify the known methods so that the dust is removed dry and wet washing with the formation of waste water in the gas cleaning is eliminated. According to the invention, this is achieved in the process mentioned at the outset by passing the dust-containing gas from the separator through a cracking chamber, with the gas contained in the cracking chamber with the addition of gaseous oxygen in the temperature range from 800 to 1200 ° C. and below the temperature of the ash melting point Hydrocarbons largely splits and thereby reduces the content of the higher hydrocarbons (C _{β +} hydrocarbons) in the gas to at most 10 wt .-% of the content of these higher hydrocarbons in the gas coming from the separator, that the gas coming from the cracking chamber is cooled , the cooled gas is passed through a dedusting device and fly dust is separated, that the cooled and dedusted gas is passed through at least one bed or a reactor with granular solids which bind pollutants and that the gas is then ■ dedusted. Due to the conditions in the cracking chamber and the conditions in the gas cleaning, the condensation and sublimation of the higher hydrocarbons (C ₆ ) does not take place in the downstream gas cleaning devices.

In the solid fuels to be gasified, it can e.g. B. are municipal or industrial waste, biomass or coal of various types. When municipal waste is gasified, it is usually first sorted before gasification, with metal and glass parts in particular being separated out. The remaining waste is then crushed, e.g. B. to piece sizes of at most 70 mm before it is gasified. To increase the calorific value of the gas coming from the gasification reactor, the solid fuels can be dried before gasification.

No liquid residues are produced in the process according to the invention. The ash drawn off from the lower region of the gasification reactor is usually so inert that it is e.g. B. is still usable for road construction, but at least the ash is easy to deposit. The airborne dust accumulating in the dedusting device can contain heavy metals and is then disposed of in the usual way. Appropriately, one burns or gasses at least a part of the flying dust in a combustion chamber at temperatures in the range of 1000 to 1500 ° C. It is advisable to add the gaseous products formed in the combustion chamber to the gasification reactor.

Design options of the method are explained with the aid of the drawing. It shows 1 shows the flow diagram of a first method variant and FIG. 2 shows the flow diagram of a second method variant.

According to FIG. 1, the solid fuels to be gasified are fed in line (1) to a gasification reactor (2), where they come into contact with hot gases and particles in the state of the circulating fluidized bed. Oxygen-containing fluidizing gas is introduced in line (3) and passed through a distribution chamber (4) with a grate (5) into the fluidized bed of the reactor (2). The oxygen-old gas of line (3) can be, for example, air or air enriched with 0 ₂ . The gasification in the reactor (2) takes place at temperatures of 700 to 1000 ° C and mostly at temperatures of at least 800 ° C. Ash is drawn off through line (6) and, if necessary, is deposited after removal of metal components or for further use, e.g. B. in road construction.

Leaves at the top of the reactor (2)

Gas-solid mixture the reactor through the channel (8) and flows into a cyclone separator (9), from which dust-containing fuel gas is withdrawn through the line (10). Solids accumulating in the separator (9) are led through the line (11) back into the lower region of the reactor (2).

The dust-containing gas of line (10) contains condensable hydrocarbons and mostly carbon-containing fly dusts. It is important to at least largely eliminate the higher hydrocarbons (C ₆₊ ) and convert them into substances that do not condense at the given temperatures and partial pressures. For this purpose, the gas is led through a Gap chamber (12), which one through line (13) 0 ₂ -containing gas, for. B. air, oxygen-enriched air or technically pure oxygen. Temperatures in the range from 800 to 1200 ° C and mostly 900 to 1100 ° C are ensured in the gap chamber (12). It is important here that the temperature and the residence time in the cracking chamber (12) are selected so that the formation of liquid slag is avoided and at the same time an adequate cracking of the C _{β +} hydrocarbons is ensured.

The gas coming in the line (15) from the gap chamber (12) contains various types of solids and ash particles, which are referred to here as flying dust. In a waste heat boiler (16), the gas is cooled to temperatures of about 150 to 300 ° C and then there is one through line (17)

Dedusting device (18). This can be, for. B. can be a fabric or electrostatic filter. The resulting dust, which usually contains heavy metals, is drawn off in line (19), a part of which can be led to a combustion chamber (21) on the transport route (20). The remaining airborne dust is removed from the process through line (22).

One leads the combustion chamber (21) through line (24) oxygen-containing gas, for. B. air, with 0 ₂ enriched air or technically pure oxygen and burns the supplied dust at temperatures in the range of 1000 to 1500 ° C. The resulting solid or liquid and gaseous combustion products are put together in the upper area of the reactor (2), where they are taken up by the fluidized bed. Deviating from Fig. 1, liquid slag can withdrawn from the combustion chamber (21) so that it does not get into the reactor (2), see FIG. 2.

From the dedusting device (18), a gas is drawn off in the line (25) which still has a disruptive content of pollutants. These pollutants are e.g. B. mercury, chlorine and sulfur compounds. In order to remove these pollutants to a large extent, the gas is first passed through an indirect cooler (26) and the temperature which is favorable for the subsequent treatment is, for. B. in the range of 100 to 150 ° C. The cooled gas is passed through line (27) for cleaning, avoiding the formation of waste water. In one or more beds or reactors, the gas to be cleaned is brought into contact with granular adsorbents. These adsorbents can e.g. B. in a fixed bed, moving bed or fluidized bed or you can use an entrained flow reactor.

In the drawing, a moving bed reactor (30) is shown in a schematic representation, which one through the line

(31) feeds granular adsorbent material which forms a bed (33) in the reactor (30) which slowly moves downwards. The bed to be cleaned flows through the bed approximately in a horizontal direction. The gas leaves the reactor (30) through line (35) and is used for dedusting through the filter

(36) performed, for. B. can be a fabric or electrostatic filter. Cleaned gas leaves the filter

(36) in line (37). The loaded adsorbent coming from the reactor (30) is discharged in line (38) with the solids separated in the filter (36) in the line

(39) mixed and subtracted. When selecting and using suitable, known adsorption materials, there are in particular the following options: hydrated lime, activated carbon, hearth furnace coke or zeolites. The mercury removal using a low-aluminum zeolite is described in EP patent 638 351.

In the flow diagram of FIG. 2, the reference numbers already mentioned together with FIG. 1 have the meaning explained there. According to FIG. 2, the pollutant-containing gas is fed to line (27) to a spray absorber (40), to which lime milk and possibly other adsorbents are fed through line (41). Gas and solids flow through line (42) to a filter (43), which is e.g. B. can be a fabric or electrostatic filter. Purified gas passes in line (44) to an adsorber (46) for the separation of mercury, e.g. B. in a zeolite fixed bed, as described in EP patent 638 351. Chloride-containing solids are drawn off in line (45). In the combustion chamber (21), liquid slag is drawn off through line (23) and the combustion gas is passed through line (32) into the reactor (2).

For example:

Residual municipal waste is fed to a process according to FIG. 2. The following data are partially calculated. The residual waste, which is delivered in an amount of 7500 kg / h, contains 24.5% by weight moisture and 30% by weight ash. This waste is first dried to 5% by weight res moisture and then gasified in the reactor (2) at 900 ° C. and with the supply of 6230 Nm ³ / h of air. 13,000 Nm ^{3 of} gas flow through the line (10) per hour, the gas contains 48 g / Nm ^{3 of} dust and 1% by volume C _{6 *} hydrocarbons. The residence time of the gas in the gap chamber (12) is 1.5 seconds, air is supplied through line (13) and an outlet temperature of 1000 ° C. is reached. The content of C ₆₊ hydrocarbons in line (15) is only 0.1% by volume. 400 kg / h of dust are fed through the line (20) into the combustion chamber (21), which is fed with 1860 Nm ³ / h of air and in which 1300 ° C. is reached. Lime milk is added to the spray absorber (40) and the outlet temperature is kept at 160 ° C. The adsorber (46) contains a fixed zeolite bed for mercury removal.

Claims

claims

1. A process for the gasification of solid fuels in the circulating fluidized bed, the fuels being gasified in a gasification reactor with the supply of oxygen-containing gas at temperatures in the range from 700 to 1000 ° C., a gas-solid mixture being fed to a separator from the upper area of the gasification reactor , from which the separator derives dust and hydrocarbons including higher hydrocarbons with more than 6 carbon atoms in the molecule with a calorific value of 2000 to 8000 kJ / m ³ and separated solids and at least partially returns the solids to the lower area of the gasification reactor , characterized in that the dust-containing gas is passed from the separator through a cracking chamber, the hydrocarbons contained in the gas being largely split and in the cracking chamber with the addition of gaseous oxygen in the temperature range from 800 to 1200 ° C and below the temperature of the ash melting point the content of the higher hydrocarbons (C _β- hydrocarbons) in the gas is reduced to a maximum of 10% by weight of the content of these higher hydrocarbons in the gas coming from the separator by cooling the gas coming from the cracking chamber, the cooled gas by a dedusting device conducts and separates flight dust, that one conducts the cooled and dedusted gas through at least one bed or a reactor with granular solids binding pollutants and that the gas is then dedusted.

2. The method according to claim 1, characterized in that at least part of the deducted from the dedusting fly dust in a combustion chamber at temperatures in the range of 1000 to 1500 ° C with the addition of 0 ₂ -containing gas.

3. The method according to claim 2, characterized in that the gaseous products formed in the combustion chamber are mixed with the solid-containing gas formed in the gasification reactor.