WO2009050494A2

WO2009050494A2 - Production of fuel from refuse

Info

Publication number: WO2009050494A2
Application number: PCT/GB2008/003548
Authority: WO
Inventors: Kenneth Leslie Wyatt
Original assignee: Moulson Process Plant Limited; Wyatt, Karen
Priority date: 2007-10-20
Filing date: 2008-10-20
Publication date: 2009-04-23
Also published as: WO2009050494A3; GB0720591D0

Abstract

The invention provides a process for the production of fuel from refuse, the process comprising the steps of: (a) providing refuse that has a calorific value; (b) heating the refuse so as to chemically decompose it to produce off gas that comprises carbon monoxide and carbon dioxide; and (c) contacting the off gas obtained in step (b) with incandescent carbon-based char in the presence of water, in the form of steam, and oxygen so as to produce water gas comprising hydrogen, carbon dioxide and carbon monoxide. Preferably the water gas is subsequently converted to alcohol, such as methanol or ethanol.

Description

PRODUCTION OF FUEL FROM REFUSE

The present invention relates to processes for the production of fuel from refuse, in particular processes for the production of fuel, such as water gas, hydrogen, or alcohol (such as methanol or ethanol), from industrial or domestic refuse that has a calorific value, and to related apparatus for the production of fuel from refuse.

Disposing of refuse produced both industrially and domestically remains a serious problem. Disposal into landfill sites uses up ever increasing amounts of land, and landfill sites are often perceived as a health and environmental hazard. Although recycling of refuse is becoming more widespread, it is not a complete solution to the problem.

Incineration of refuse has also been considered as an option. However, this commonly leads to the production of undesirable and toxic chemicals.

Therefore there is a need for a process that will permit clean disposal of refuse. It would also be desirable to obtain a useful product from the refuse disposal, which would alleviate the need to separate refuse into recyclable and non-recyclable materials.

The present invention provides, in a first aspect, a process for the production of fuel from refuse, the process comprising the steps of: (a) providing refuse that has a calorific value;

(b) heating the refuse so as to chemically decompose it to produce off gas that comprises carbon monoxide and carbon dioxide; and

(c) contacting the off gas obtained in step (b) with incandescent carbon-based char in the presence of water, in the form of steam, and oxygen so as to produce water gas comprising hydrogen, carbon dioxide and carbon monoxide. This process is environmentally friendly, as it permits the disposal of refuse whilst avoiding toxic or otherwise undesirable side products. In particular, the high temperature used in step (c) to produce the water gas ensures that the undesirable and toxic chemicals associated with the incineration of refuse are not present. The process is also advantageous in that it provides a useful fuel product from the refuse. The water gas may be used directly as a fuel, or the hydrogen can be isolated for use as a fuel.

Preferably, some or all of the water gas may subsequently be converted to an alcohol, such as methanol or ethanol, which may be used as fuel.

The process also is efficient, as it permits recycling within the process of products/by-products obtained in of one or more of its steps.

Any refuse that has a calorific value, in other words any refuse that produces heat during combustion, can be used in the present process. The refuse may be domestic or industrial. In one embodiment, the refuse has a calorific value of lkJ/kg or higher, such as 50kJ/kg or higher, e.g. 100kJ/kg or higher.

The refuse may comprise one or more materials selected from: paper; cardboard; biomass; plastics materials and elastomeric materials, including halogenated plastics material and vehicle tyres; and food waste.

The refuse may include water, for example the refuse could in part be a sludge or slurry, such as a wastewater sludge cake, or may be waste food that contains water. It is preferred that the water is present at a level less than that which would negate the calorific value of the refuse. In step (b) the refuse may be heated to any suitable temperature. Preferably, the refuse is heated to a temperature of 400⁰C or higher, e.g. from 400⁰C to 1000°C or higher, such as 45O⁰C or higher, e.g. from 500°C to 1000°C or higher; for example it may be heated to 600⁰C or higher, or 65O⁰C or higher, such as 700°C or higher, or 75O⁰C or higher, or 800⁰C or higher, e.g. from 800°C to 1500⁰C. In one embodiment the refuse is heated to 1000°C or higher, such as from 1000°C to 1500°C.

In one embodiment, in step (b) the refuse is heated under pressure, i.e. at a pressure greater than atmospheric pressure. For example, the refuse may be heated under a pressure of from 15OkPa to 100OkPa, such as from 15OkPa to 90OkPa or from 15OkPa to 85OkPa or from 15OkPa to 80OkPa. For example, the refuse may be heated under a pressure of from 20OkPa to 90OkPa, e.g. from 25OkPa to 85OkPa, such as from 30OkPa to 80OkPa.

The off gas preferably comprises carbon monoxide and carbon dioxide in an amount of 75% by volume or more, e.g. 80% by volume or more, such as 85% by volume or more.

However, the off gas suitably also includes other gases, for example hydrogen and/or gaseous hydrocarbons, such as methane.

In one embodiment the off gas comprises carbon monoxide, carbon dioxide and hydrogen. In one embodiment the off gas comprises carbon monoxide, carbon dioxide and methane. In one embodiment the off gas comprises carbon monoxide, carbon dioxide, hydrogen and methane.

In one embodiment the off gas further comprises one or more other hydrocarbons in addition to methane. In step (b) pyrolysis may occur. Pyrolysis is a chemical process in which the refuse is converted to one or more products, including an off gas product, substantially by heat. Accordingly, substantially no reactions occur by the presence of other components; e.g. a catalyst or oxygen.

Accordingly, in one embodiment, step (b) is carried out in the presence of substantially no oxygen, i.e. there is pyrolysis; in particular step (b) may be carried out in the substantial absence of air.

For example, an amount of oxygen of 5% of stoichiometric or less, such as 3% or less or 2% or less or 1% or less or 0.5% or less of stoichiometric may be present.

When pyrolysis is carried out, this may, for example, be at temperatures of from 400 to 500⁰C. In such an embodiment, recoverable materials such as glass and metal do not have to be sorted and separated from the refuse prior to carrying out step (b) as they will pass through step (b) without decomposition and can be recovered from the solid by-product.

In another embodiment, in step (b) the refuse is heated in the limited presence of oxygen, preferably less than stoichiometric amounts of oxygen, so as to achieve chemical decomposition. In other words, the refuse is heated in an amount of oxygen of less than 100% of the amount required for combustion. This heating may be described as carbonation or gasification.

Therefore in the present invention the refuse may, for example, be heated in an amount of oxygen of from 1 to 99% of the amount required for combustion. Preferably, the refuse is heated in an amount of oxygen of 90% of stoichiometric or less, such as 75% of stoichiometric or less, e.g. 60% of stoichiometric or less, such as 50% of stoichiometric or less. In one embodiment, the oxygen is present in an amount of 40% of stoichiometric or less, such as 30% of stoichiometric or less, e.g. 20% of stoichiometric or less, such as 10% of stoichiometric or less, e.g. 9% of stoichiometric or less.

In one embodiment, the oxygen is present in an amount of more than 30 and up to 90% of stoichiometric, such as from 35 to 80% of stoichiometric, e.g. from 40 to 70% of stoichiometric, such as from 45 to 65Ψo of stoichiometric.

Because some oxygen will almost inevitably be present in any system, partial oxidation will usually occur in step (b) , regardless as to whether step (b) is pyrolysis, or carbonation or gasification.

When some degree of oxidation occurs, step (b) will produce off gas that comprises carbon monoxide and carbon dioxide, together with a solid byproduct, in particular a solid by-product that comprises carbon-based char. This off gas will generally be mainly carbon monoxide and carbon dioxide, for example it may include carbon monoxide and carbon dioxide at a level of 80% by volume or more, such as 90% by volume or more.

The solid by-product that comprises carbon-based char may be disposed of.

However, some or all of the solid by-product that comprises carbon-based char may be used in step (c). In particular, some or all of the solid byproduct that comprises carbon-based char may be used to form a bed of carbon-based char which is used in step (c). In step (b) steam may, optionally, be introduced. This steam may be a product of the downstream processes in the present process that is fed back to step (b) , and/or may be introduced as a separate feed from elsewhere.

In another embodiment, in step (b) there is substantially no steam added.

Step (b) may be carried out in any suitable unit, e.g. a thermal treatment unit. Conventional thermal treatment equipment may preferably be used.

In one embodiment, a rotary thermal treatment unit, such as a rotary kiln or a rotary hearth furnace, may be used for step (b) .

The water gas production of step (c) may be carried out in any suitable water gas production unit. Water gas production is well known and any suitable unit known in the art, such as a water gas furnace, may be used. Detailed information on water gas production is available in the book "Fuel Solid, Liquid and Gaseous" by J. S. S. Brame and J. G. King, chapters XVI and XVII.

In particular, the water gas production of step (c) may be carried out in a water gas generator furnace comprising a fuel bed, which is a bed of the incandescent carbon-based char. The bed may be supported on a suitable grate. The furnace may have a refractory-lined steel casing. Supplies for the oxygen, the steam and the fuel for the fuel bed may be provided.

In step (c) the carbon-based char may, for example, be coke, anthracite or charcoal. Preferably the carbon-based char is coke.

The carbon-based char in step (c) may comprise, consist essentially of or consist of carbon-based char by-product from step (b) . In one embodiment 10wt% or more of the carbon-based char in step (c) is carbon-based char by-product from step (b) , such as 20wt% or more, or 30wt% or more, or 40wt% or more, or 50wt% or more.

In one embodiment the carbon-based char in step (c) includes some carbon-based char by-product from step (b) but also includes some separately supplied carbon based-char, e.g. coke. For example, 25wt% or more, such as 50wt% or more or 75wt% or more of the carbon-based char used in step (c) may be separately supplied product rather than by- product from step (b) .

In another embodiment the carbon-based char used in step (c) comprises substantially no carbon-based char by-product from step (b) .

The carbon-based char is preferably present as a bed through which the off gas is passed.

Further carbon-based char may be added as required during the process to keep it at a suitable level for the water gas reaction in step (c) .

In step (c) the oxygen may be provided in pure form, substantially pure form or in the form of a mixture with other gases, such as in the form of air.

In one embodiment, the oxygen is provided in the form of oxygen- enriched air. For example, air may have additional oxygen added to it, e.g. from a pressure swing absorption oxygen generator, prior to the air being fed into the water gas production unit.

Oxygen enrichment may be advantageous in that it can reduce the nitrogen content of the water gas produced, increasing its calorific value. This reduction in nitrogen content of the water gas can also be beneficial in terms of the design of any downstream processing of the water gas, for example in the design of an alcohol (e.g. methanol or ethanol) synthesis unit to process the water gas.

The oxygen is preferably introduced at pressure sufficient to drive the gases through the process.

The oxygen may be pre-heated, e.g. pre-heated to 200⁰C or higher, such as 300⁰C or higher, for example 400⁰C or higher. This provides an improved yield of water gas.

The oxygen may be introduced below the carbon-based char. Preferably, the oxygen is blasted into the water gas production unit below the carbon- based char.

The off gas from step (b) may be introduced below the carbon-based char bed.

In step (c) some or all of the water is provided in the form of steam. Additionally, water vapour may be present from step (b) . The introduction of steam can prevent slagging and can enrich the hydrogen content of the resultant water gas.

Preferably, steam is introduced below the carbon-based char. In one embodiment, the steam is introduced with the oxygen.

The steam may be introduced at relatively low pressure; preferably the pressure is sufficient to drive the gases through the char bed. In one embodiment, the off gas, the oxygen, and the steam are each introduced below the carbon-based char bed.

The steam may be pre-heated, e.g. pre-heated to 200^ϋC or higher, such as 300^ϋC or higher, for example 400^ϋC or higher.

The carbon-based char may be red hot or white hot. Suitably, it may be at a temperature of 1000⁰C or higher, e.g. from 1000 to 1600⁰C or higher, such as HOO⁰C or higher; preferably the carbon-based char is at a temperature of 1200⁰C or higher, for example 125O⁰C or higher, such as 1300°C or higher; e.g. 135O⁰C or higher.

Although pressurised oxygen and/or steam may introduced at a pressure sufficient to drive the gases through the char bed, high pressures are not required in step (c).

In one embodiment, step (c) uses pressure of 45OkPa or less, such as 40OkPa or less, or 30OkPa or less, or 20OkPa or less, or 15OkPa or less.

In one embodiment, in step (c) a pressure of greater than atmospheric pressure may be used. For example, step (c) may use a pressure of from 105kPa to 50OkPa, such as from HOkPa to 45OkPa or from 12OkPa to 40OkPa or from 13OkPa to 35OkPa. For example, in step (c) a pressure of from 14OkPa to 30OkPa, e.g. from 14OkPa to 27OkPa, such as from 15OkPa to 25OkPa may be used.

The composition of the resultant water gas can be controlled by several of the reaction conditions. In particular, the ratio of off gas to carbon-based char; the levels of steam introduced; and the levels of oxygen used (e.g. in the form of oxygen enriched air) will affect the resultant water gas composition. For example, the ratio of steam to oxygen can be adjusted to control the gas composition of the resultant water gas, as desired.

The water gas produced in step (c) preferably comprises a majority of hydrogen and carbon monoxide, with a minority of carbon dioxide. For example, 70% or more by volume of the water gas may be hydrogen and carbon monoxide, such as 80% or more by volume (for example from 85 to 95% by volume) , e.g. 90% or more by volume.

The water gas produced in step (c) may comprise, in addition to hydrogen, carbon monoxide, and carbon dioxide, other gases. For example, the water gas may comprise nitrogen and/or gaseous hydrocarbons, such as methane. Preferably such other gases are present at levels of 10% by volume or less, for example 8% by volume or less, such as 7% by volume or less, e.g. 5% by volume or less.

The water gas reaction of step (c) will also result in the production of a solid by-product e.g. solid by-product that comprises ash.

The solid by-product may be disposed of. Alternatively, solid by-product may be transferred to useful applications, e.g. for building aggregate. In one embodiment solid by-product from step (c) is combined with solid byproduct from step (b) and either disposed of or transferred to useful applications.

Some of the water gas produced in step (c) may be recycled back into step (b) . For example, up to 50% by volume, e.g. up to 25%, such as from 1 to 20%, of the water gas produced in step (c) may be recycled back into the chemical decomposition step (b) . In one embodiment, the water gas production unit in which step (c) is carried out and the thermal treatment unit in which step (b) is carried out are arranged such that heat exchange can take place between these units. Accordingly, in one embodiment, heat is exchanged between the water gas reaction in step (c) and the chemical decomposition in step (b) .

In one embodiment, the thermal treatment unit is located around the outside of water gas production unit, for example the thermal treatment unit and water gas production unit may be constructed as concentric cylinders, with the thermal treatment unit being the outer cylinder, such that heat exchange can take place between the two units.

In one embodiment, some or all of the water gas produced in step (c) is collected for use as fuel. In this regard, the water gas itself may be collected for use as fuel. Alternatively, one or more isolation steps may be carried out to isolate the hydrogen for use as fuel.

The water gas produced in step (c) that is collected for use as fuel is preferably cleaned prior to its use as fuel. For example, gas cleaning to remove impurities, such as chlorine containing compounds (e.g. HCl) and sulphur containing compounds (e.g. SO₂) , and/or particulates such as dust, may be carried out.

Various methods of gas-cleaning and gas-cleaning units are known in the art and can be used; these may, for example involve the use of washers/scrubbers, filters, precipitators, and/or adsorbents. In one embodiment, the water gas is cleaned using a wet gas-cleaning process, such as washing with water or an aqueous solution. In particular, conventional aqueous scrubbing can be used. Washing with organic solvents may also be considered as an alternative to aqueous solvents. In a preferred embodiment of the invention, some or all of the water gas obtained in step (c) is subsequently converted to an alcohol, such as a Cl- C6 alcohol, e.g. a Cl, C2, C3 or C4 alcohol; preferably the alcohol is methanol or ethanol.

The result of carrying out the water-gas reaction (c) following the chemical decomposition in step (b) is to increase the amount of hydrogen. This is beneficial for the subsequent production of alcohol such as methanol, as in the synthesis a higher stoichiometric amount of hydrogen as compared to carbon monoxide is required.

In one embodiment, some or all of the water gas produced in step (c) is used to produce an alcohol such as methanol or ethanol. In this embodiment, the process preferably further comprises the following steps: (d) carrying out a gas-cleaning procedure on water gas obtained in step (c) ; and

(e) catalytically converting the cleaned water gas obtained in step (d) to an alcohol such as methanol or ethanol.

Accordingly, either (i) solely gaseous fuel, (ii) some gaseous fuel and some liquid fuel, or (iii) solely liquid fuel can be obtained by the process of the present invention.

Solely gaseous fuel can be obtained by only carrying out steps (a) to (c) ; some gaseous fuel and some liquid fuel can be obtained by carrying out steps (a) to (e) , with collection of some water gas after step (c) whilst allowing some water gas to be used in steps (d) to (e) ; and solely liquid fuel can be obtained by carrying out steps (a) to (e) without collection of water gas after step (c). The water gas produced in step (c) may be passed through a heat exchanger before step (d) , and the heat obtained may be used to pre-heat the cleaned water gas when it is fed to step (e) . One or both of steps (b) and (c) may be controlled so as to achieve a gas composition optimised for alcohol (e.g. methanol or ethanol) production in step (e). For example, the conditions in step (b) may be controlled so as to control the amounts of carbon monoxide and carbon dioxide in the gas produced, and/or conditions in step (c) , such as the amount of oxygen and water, may be controlled so as to control the amounts of hydrogen, carbon dioxide and carbon monoxide in the water gas produced.

In step (d) the water gas is cleaned to remove impurities. For example, impurities such as chlorine containing compounds (e.g. HCl) and sulphur containing compounds (e.g. H₂S, SO₂) may be removed. Particulates such as dust may be removed.

Step (d) is carried out in a gas-cleaning unit. Various methods of gas- cleaning and gas-cleaning units are known in the art and can be used; these may, for example involve the use of washes/scrubbers, filters, precipitators, and/or adsorbents.

In one embodiment, the water gas is cleaned using a wet gas-cleaning process, such as washing with water or an aqueous solution. In particular, conventional aqueous scrubbing can be used. Washing with organic solvents may also be considered.

Step (e) is carried out in a catalytic alcohol (e.g. methanol or ethanol) production unit. Catalytic production of alcohol (e.g. methanol or ethanol) from a synthesis gas which comprises carbon monoxide and hydrogen, and optionally carbon dioxide, is well known. Any known catalytic alcohol (e.g. methanol or ethanol) production plant may be used in step (e) . Any suitable catalyst may be used in step (e) to catalyze the production of alcohol (e.g. methanol or ethanol) from the gas. Zinc oxide/chromium oxide catalysts or copper oxide catalysts, which may contain additional oxides, can be mentioned for use. Preferably, copper based catalysts are used. Catalysts known for use in this reaction include catalysts based on copper, zinc and aluminium; zirconia-supported copper catalysts; and ceria-supported copper catalysts.

The reaction in step (e) may be carried out under any suitable pressure. For example, pressures of from 1 to 50MPa, preferably from 3 to 25MPa, such as from 4 to lOMPa may be used.

The reaction in step (e) may be carried out at any suitable temperature. For example, temperatures of 200⁰C or higher may be used, preferably from 200 to 400°C, such as 200 to 300⁰C, e.g. about 250⁰C.

In one embodiment, step (e) is carried out at a pressure of from 3 to 5MPa and a temperature of from 225 to 275⁰C; such as a pressure of about 4MPa and a temperature of about 250⁰C.

In step (e) the cleaned water gas may be fed under pressure to a reaction system of one or several reactors, wherein in each of the reactors a partial conversion to alcohol (e.g. methanol or ethanol) is achieved.

The alcohol (e.g. methanol or ethanol) product produced in step (e) may have a purity of 60% or more, such as 65% or more, e.g. 70% or more. Preferably, most or all of the remaining product is water. The alcohol (e.g. methanol or ethanol) produced in step (e) may be collected and stored for later use, or may be transferred directly to a desired application.

Preferably, the alcohol (e.g. methanol or ethanol) produced in step (e) is firstly distilled to increase its purity; for example it may be distilled to have a purity of 90% or more, such as 95% or more, e.g. from 95 to 97%.

The production of alcohol (e.g. methanol or ethanol) in step (e) also results in the production of by-products, specifically off gas. Advantageously, the high temperature used in step (c) and (e), and the cleaning of step (d), ensures that the undesirable and toxic chemicals associated with the incineration of refuse are not present in this off gas.

Therefore the process of the present invention is beneficial in that it produces a useful fuel product and a non toxic off gas. Additionally, the by-products of the process, such as steam and off gas, can be recycled within the process.

Some of the off gas by product produced in step (e) may be recycled back into the chemical decomposition step (b) . For example, up to 50% by volume, e.g. up to 25%, of the off gas produced in step (e) may be recycled back into the chemical decomposition step (b) .

The alcohol (e.g. methanol or ethanol) production reaction in step (e) may also result in the production of high-pressure steam as a by-product. This high-pressure steam may be used to generate power. Alternatively or additionally, some or all of the steam may be fed to the water gas reaction in step (c). There may be surplus steam that can be fed to other applications. The process of the present invention may be carried out continuously or batch wise.

The present process is advantageous because the alcohol (e.g. methanol or ethanol) produced in step (e) is a readily storable liquid fuel which therefore gives flexibility as to its subsequent usage.

Uses of methanol include power generation and fuel for vehicles. Some existing vehicles have been converted to be methanol powered and more methanol powered vehicles can be expected in the future. Methanol is advantageous in that it can be used as a fuel for both petrol and diesel engines; it is also low hazard and therefore can be easily stored for later use. It is also an environmentally clean fuel.

Ethanol is also widely used as a fuel, in particular for vehicles. Vehicles that run on ethanol are known; for example ethanol powered cars are common in Brazil. Existing spark-ignited engines will commonly operate well with mixtures of 10% ethanol.

The present invention also provides, in a second aspect, an apparatus for the production of fuel from refuse, the apparatus comprising: (I) a thermal treatment unit for carrying out chemical decomposition of the refuse with the resultant production of off gas that comprises carbon monoxide and carbon dioxide; and

(II) a water gas production unit for contacting the off gas obtained in thermal treatment unit (I) with incandescent carbon-based char in the presence of water, in the form of steam, and oxygen so as to produce water gas comprising hydrogen, carbon dioxide and carbon monoxide; wherein the thermal treatment unit and water gas production unit are connected such that off gas produced in the thermal treatment unit is fed to the water gas production unit.

In one embodiment, the thermal treatment unit (I) is selected from conventional thermal treatment equipment, such as rotary kilns or rotary hearth furnaces.

The water gas production unit (II) may be a water gas furnace. This may be a water gas generator furnace comprising a fuel bed, which is a bed of the incandescent carbon-based char. The bed may be supported on a suitable grate. The furnace may have a refractory-lined steel casing. Supplies for the oxygen, the steam and the fuel for the fuel bed may be provided.

In one embodiment, the thermal treatment unit and water gas production unit are connected such that some of the water gas produced in the water gas production unit can be fed back to the thermal treatment unit.

In one embodiment, the water gas production unit and the thermal treatment unit are arranged such that heat exchange can take place between these units.

In one such embodiment, the thermal treatment unit is located around the outside of water gas production unit, for example the thermal treatment unit and water gas production unit may be constructed as concentric cylinders, with the thermal treatment unit being the outer cylinder, such that heat exchange can take place between the two units.

Alternatively, the thermal treatment unit and the water gas production unit may be distinct and separate units. In one embodiment, the water gas production unit includes a water gas outlet via which some or all of the water gas produced may be collected for use as fuel. In this regard, the water gas itself may be collected, or one or more isolation steps may be carried out to isolate the hydrogen.

In such an embodiment, the apparatus may further comprise a gas- cleaning unit (Ha) for cleaning the water gas obtained in water gas production unit (II) prior to its use as fuel, wherein the water gas production unit and the gas-cleaning unit are connected such that water gas produced in the water gas production unit is fed to the gas-cleaning unit.

In one embodiment, some or all of the water gas produced in water gas production unit (II) may be used to produce alcohol, such as a C1-C6 alcohol, e.g. a Cl , C2, C3 or C4 alcohol; preferably the alcohol is methanol or ethanol. In one embodiment, therefore, some or all of the water gas produced in water gas production unit (II) may be used to produce methanol.

Accordingly the apparatus may further comprise:

(III) a gas-cleaning unit for cleaning water gas obtained in water gas production unit (II) ; and

(IV) a catalytic alcohol production unit for catalytically converting the cleaned water gas obtained in gas-cleaning unit (III) to alcohol (e.g. methanol or ethanol); wherein the water gas production unit and the gas-cleaning unit are connected such that water gas produced in the water gas production unit is fed to the gas-cleaning unit, and wherein the gas-cleaning unit and the catalytic alcohol production unit are connected such that cleaned water gas produced in the gas-cleaning unit is fed to the catalytic alcohol production unit.

The catalytic alcohol production unit is suitably for catalytically converting the cleaned water gas obtained in gas-cleaning unit (III) to a C1-C6 alcohol, such as Cl, C2, C 3 or C4 alcohol; in particular to methanol or ethanol.

The apparatus may further comprise a heat exchanger to obtain heat from the water gas produced in the water gas production unit (II) before it enters gas-cleaning unit (III) . This heat exchanger may be arranged such that it can transfer heat back to the cleaned water gas produced in gas- cleaning unit (III) before it enters catalytic alcohol (e.g. methanol or ethanol) production unit (IV) .

The gas-cleaning unit (III) may comprise one or more gas-cleaning apparatus, which may be selected from washers/scrubbers, filters, precipitators, and adsorbents.

The catalytic alcohol (e.g. methanol or ethanol) production unit (IV) may comprise a reaction system of one or several reactors, wherein in each of the reactors a partial conversion to alcohol (e.g. methanol or ethanol) is achieved.

The catalytic alcohol (e.g. methanol or ethanol) production unit (IV) may comprise an alcohol (e.g. methanol or ethanol) outlet via which some or all of the alcohol (e.g. methanol or ethanol) produced may be transferred for subsequent use as fuel.

The apparatus may further comprise: (V) an alcohol distillation unit where alcohol (e.g. methanol or ethanol) produced in catalytic alcohol production unit (IV) may be distilled to a higher degree of purity, wherein the catalytic alcohol production unit and the alcohol distillation unit are connected such that alcohol (e.g. methanol or ethanol) produced in the catalytic alcohol production unit is fed to the alcohol distillation unit.

Preferably, the alcohol distillation unit (V) is fed with alcohol (e.g. methanol or ethanol) from the catalytic alcohol production unit (IV) via the alcohol outlet.

The apparatus may further comprise:

(VI) an alcohol storage unit where alcohol (e.g. methanol or ethanol) produced in catalytic alcohol production unit (IV) may be collected and stored for later use, wherein the catalytic alcohol production unit and the alcohol storage unit are connected such that alcohol (e.g. methanol or ethanol) produced in the catalytic alcohol production unit is fed to the alcohol storage unit.

Preferably, the alcohol storage unit (VI) is connected to the catalytic alcohol production unit (IV) via the alcohol distillation unit (V) , such that the alcohol storage unit (VI) is fed with alcohol (e.g. methanol or ethanol) from the catalytic alcohol production unit (IV) that has firstly been purified in the alcohol distillation unit (V) .

In one embodiment, the catalytic alcohol production unit (IV) and the thermal treatment unit (I) are connected, such that some of the off gas by product produced in the catalytic alcohol production unit (IV) may be recycled back into the thermal treatment unit (I) . The apparatus of the second aspect may be used to carry out the process of the first aspect.

The invention will now be further described, by means of example only, with reference to the drawing in which:

Figure 1 is a schematic diagram illustrating the apparatus and process of the invention.

Figure 1 shows an apparatus for the production of fuel from refuse. The apparatus comprises a thermal treatment unit 1 for carrying out chemical decomposition of the refuse with the resultant production of off gas that comprises chiefly carbon monoxide and carbon dioxide. The thermal treatment unit is a conventional thermal treatment unit that can decompose the refuse to give off gas and char. The thermal treatment unit 1 has a refuse inlet 2 and a limited air inlet 3, as well as an off gas outlet 4 and a char outlet 5.

The apparatus also includes a water gas production unit 6 for contacting the off gas obtained in thermal treatment unit 1 with a bed of incandescent coke 7 in the presence of water, in the form of steam, and oxygen so as to produce water gas comprising hydrogen, carbon dioxide and carbon monoxide. The water gas production unit is a conventional water gas production unit that can react the off gas that comprises carbon monoxide and carbon dioxide to give water gas and ash.

The water gas production unit 6 is connected to the thermal treatment unit via off gas outlet 4 such that off gas produced in the thermal treatment unit 1 is fed to the water gas production unit 6 below the bed of coke 7. The water gas production unit 6 is provided with a coke inlet 8 and an oxygen inlet 9. The oxygen inlet 9 is fed with oxygen or oxygen enriched air that results from air stream 9a passing through oxygen PSA unit 9b to enrich the air with oxygen.

The water gas production unit 6 is suitably provided with a water gas recycle outlet 10 which is connected to the thermal treatment unit 1 such that some of the water gas produced in the water gas production unit 6 can be fed back to the thermal treatment unit 1.

The water gas production unit 6 is also provided with a water gas outlet 11 and an ash outlet 12.

The water gas production unit 6 and the thermal treatment unit 1 are arranged such that heat exchange (shown by arrows H) can take place between these units.

The water gas outlet 11 leads to water gas fuel outlet 11a, through which some or all of the water gas produced may be collected for use as fuel, and to water gas conversion outlet Hb, though which some or all of the water gas produced may be transferred to be converted to methanol.

The water gas fuel outlet Ha suitably leads to a gas-cleaning unit for cleaning the water gas obtained in water gas production unit 6 prior to its use as fuel. This may be a separate gas-cleaning unit (not shown) . Alternatively, this may be the gas-cleaning unit 14 discussed below. In this case, the water gas flows into the gas-cleaning unit 14 via water gas conversion outlet lib rather than water gas fuel outlet 11a, and then leaves the gas-cleaning unit 14 after it has been cleaned via water gas fuel outlet Ha' , through which the cleaned water gas may be collected for use as fuel. The water gas conversion outlet lib leads to heat exchanger 13 to obtain heat from the water gas produced in the water gas production unit 6.

The apparatus also includes a gas-cleaning unit 14 for cleaning the water gas obtained in water gas production unit 6. The gas-cleaning unit 14 is a conventional gas-cleaning unit that can remove impurities from gas. The gas-cleaning unit 14 shown is a water-washing based unit, but the skilled man will understand other gas-cleaning units may be used. The gas- cleaning unit 14 has a water gas inlet 15 that receives water gas from the water gas production unit 6 via the heat exchanger 13. It also has a water inlet 16 for the washing water and a water outlet 17 for the used washing water.

The gas-cleaning unit 14 also has a cleaned water gas outlet 18 for transferring the cleaned water gas back to the heat exchanger 13, where it can be heated.

The apparatus also includes a catalytic methanol production unit 19 for catalytically converting the cleaned water gas obtained from the gas- cleaning unit 14 to methanol. The catalytic methanol production unit 19 is a conventional catalytic methanol production unit that can convert gas comprising carbon monoxide and hydrogen, and optionally carbon dioxide, to methanol, with the production of off gas and steam.

The catalytic methanol production unit 19 has a cleaned water gas inlet 20 that receives cleaned water gas from the gas-cleaning unit 14 via the heat exchanger 13.

The catalytic methanol production unit 19 also has a water inlet 21, an off gas outlet 22, a steam outlet 23 and a methanol outlet 24. The off gas outlet 22 leads to off gas recycling outlet 22a, through which some or all of the off gas produced may be recycled back to thermal treatment unit 1, and off gas disposal outlet 22b, through which some or all of the off gas produced may be released for disposal.

The steam outlet 23 leads to power generation unit 25, via which power can be generated from the high pressure steam. The power generation unit has a steam outlet 26. The steam outlet 26 leads to steam recycling outlet 26a through which some or all of the steam may subsequently be recycled back to water gas production unit 6, via the oxygen inlet 9, and steam disposal outlet 26b, through which some or all of the steam produced may be released for disposal.

The apparatus further comprises a methanol distillation unit 27. The methanol distillation unit 27 has a methanol inlet 28 which receives methanol produced in catalytic methanol production unit 19 via methanol outlet 24. It also has a methanol outlet 29 which transfers purified methanol either: to a methanol storage unit (not shown) for storage until it is required; or directly to desired applications as needed.

Accordingly, in use, refuse and a limited air supply are fed into thermal treatment unit 1 where the refuse is decomposed to produce off gas and char. The off gas is transferred to water gas production unit 6, whilst the char is disposed of.

In the water gas production unit the off gas is fed under a bed of incandescent coke, together with a stream of oxygen or oxygen enriched air and steam. This results in the production of water gas, some of which may be recycled back to the thermal treatment unit 1 and some of which may be collected for use as fuel. At least some of the water gas is transferred to gas-cleaning unit 14. Any ash produced is disposed of.

The water gas that is transferred to gas-cleaning unit 14 travels via heat exchanger 13, to capture heat from the gas.

The gas-cleaning unit 14 washes the water gas to remove impurities. Some cleaned water gas may be collected for use as fuel.

At least some of the cleaned gas from the gas-cleaning unit 14 is transferred via the heat exchanger 13 so that it is heated before then being transferred to catalytic methanol production unit 19. The catalytic methanol production unit 19 is also fed with water, and contains catalyst so as to convert the water gas to methanol.

The resultant methanol is fed to methanol distillation unit 27 where it is distilled to a higher degree of purity, e.g. 95 to 97% purity.

The purified methanol may be fed via outlet 29 to a methanol storage unit, or directly to desired applications e.g. , as fuel for vehicles.

Some or all of the off gas by product may be recycled to thermal treatment unit 1. The steam by product is transferred to power generator 25 to generate power; subsequently some or all of the steam can be recycled to the water gas production unit 6.

The methanol in the methanol storage unit can be stored and then transferred as needed to desired applications, e.g. , as fuel for vehicles, or for power generation. The skilled man would understand that although a catalytic methanol production unit is described in relation to the apparatus shown in Figure 1, a catalytic ethanol production unit that can convert gas comprising carbon monoxide and hydrogen, and optionally carbon dioxide, to ethanol, with the production of off gas and steam, could equally be used. Thus the methanol production/transfer/distillation/storage apparatus could be replaced by ethanol production/transfer/distillation/storage apparatus.

Claims

1. A process for the production of fuel from refuse, ' the process comprising the steps of: (a) providing refuse that has a calorific value;

(c) contacting the off gas obtained in step (b) with incandescent carbon-based char in the presence of water, in the form of steam, and oxygen so as to produce water gas comprising hydrogen, carbon dioxide and carbon monoxide.

2. The process of claim 1 wherein some or all of the water gas obtained in step (c) is subsequently converted to an alcohol.

3. The process of claim 2 wherein the alcohol is methanol or ethanol.

4. The process of claim 2 or claim 3, wherein after step (c) the following steps are carried out: (d) carrying out a gas-cleaning procedure on water gas obtained in step (c); and

(e) catalytically converting the cleaned water gas obtained in step (d) to an alcohol.

5. The process of claim 4, wherein the catalyst used in step (e) is selected from: zinc oxide/chromium oxide catalysts and copper based catalysts.

6. The process of claim 4 or claim 5, wherein the reaction in step (e) is carried out under a pressure of from 1 to 50MPa.

7. The process of any one of claims 4 to 6, wherein the reaction in step (e) is carried out at a temperature of 200⁰C or higher.

8. The process of any one of claims 4 to 7, wherein off gas by- product is produced in step (e) and some of this off gas is recycled back into the chemical decomposition step (b) .

9. The process of any one of claims 4 to 8, wherein step (e) results in the production of high-pressure steam as a by-product and some or all of this steam is fed to the water gas reaction in step (c) .

10. The process of any one of the preceding claims wherein some of the water gas produced in step (c) is recycled back into step (b).

11. The process of any one of the preceding claims wherein in step (b) the refuse is heated in the presence of less than stoichiometric amounts of oxygen, so as to achieve chemical decomposition.

12. The process of any one of the preceding claims wherein step (b) is carried out in the presence of substantially no oxygen.

13. The process of any one of the preceding claims wherein a rotary thermal treatment unit, such as a rotary kiln or a rotary hearth furnace, is used for step (b) .

14. The process of any one of the preceding claims wherein in step (c) the steam is pre-heated to 200"C or higher.

15. The process of any one of the preceding claims wherein in step (c) the carbon-based char is at a temperature of 1000⁰C or higher.

16. The process of any one of the preceding claims wherein the water gas production of step (c) is carried out in a water gas furnace.

17. The process of any one of the preceding claims wherein in step (c) the carbon-based char is present as a bed, through which the off gas is passed.

18. The process of claim 17, wherein one or more of: (i) the off gas; (ii) the oxygen; and

(iii) the steam; is introduced below the carbon-based char bed.

19. The process of any one of the preceding claims, wherein heat is exchanged between the water gas reaction in step (c) and the chemical decomposition in step (b) .

20. An apparatus for the production of fuel from refuse, the apparatus comprising: (I) a thermal treatment unit for carrying out chemical decomposition of the refuse with the resultant production of off gas that comprises carbon monoxide and carbon dioxide; and

(II) a water gas production unit for contacting the off gas obtained in thermal treatment unit (I) with incandescent carbon-based char in the presence of water, in the form of steam, and oxygen so as to produce water gas comprising hydrogen, carbon dioxide and carbon monoxide; wherein the thermal treatment unit and the water gas production unit are connected such that off gas produced in the thermal treatment unit is fed to the water gas production unit.

21. The apparatus of claim 21, further comprising a unit for converting some or all of the water gas obtained in the water gas production unit (II) to an alcohol, such as methanol or ethanol.

22. The apparatus of claim 21 , wherein the apparatus further comprises:

(III) a gas-cleaning unit for cleaning the water gas obtained in water gas production unit; and

(IV) a catalytic alcohol production unit for catalytically converting the cleaned water gas obtained in gas-cleaning unit to alcohol; wherein the water gas production unit and the gas-cleaning unit are connected such that water gas produced in the water gas production unit is fed to the gas-cleaning unit, and wherein the gas-cleaning unit and the catalytic alcohol production unit are connected such that cleaned water gas produced in the gas-cleaning unit is fed to the catalytic alcohol production unit.

23. The apparatus of claim 22, wherein the apparatus further comprises a heat exchanger to obtain heat from the water gas produced in the water gas production unit before it enters the gas-cleaning unit.

24. The apparatus of claim 23 wherein the heat exchanger is arranged such that it can transfer heat back to the cleaned water gas produced in the gas-cleaning unit before it enters the catalytic alcohol production unit.

25. The apparatus of any one of claims 22 to 24, wherein the catalytic alcohol production unit and the thermal treatment unit are connected, such that some of the off gas by product produced in the catalytic alcohol production unit may be recycled back into the thermal treatment unit.

26. The apparatus of any one of claims 20 to 25, wherein the thermal treatment unit and the water gas production unit are connected such that some of the water gas produced in the water gas production unit can be fed back to the thermal treatment unit.

27. The apparatus of any one of claims 20 to 26, wherein the water gas production unit and the thermal treatment unit are arranged such that heat exchange can take place between these units.

28. The apparatus of any one of claims 20 to 27, wherein the water gas production unit includes a water gas outlet via which some or all of the water gas produced may be collected for use as fuel.

29. The apparatus of any one of claims 20 to 28, wherein the apparatus further comprises:

(V) an alcohol distillation unit where alcohol produced in the catalytic alcohol production unit may be distilled to a higher degree of purity, wherein the catalytic alcohol production unit and the alcohol distillation unit are connected such that alcohol produced in the catalytic alcohol production unit is fed to the alcohol distillation unit.