WO2001052972A1

WO2001052972A1 - Method and installation for purifying gases derived from waste thermolysis

Info

Publication number: WO2001052972A1
Application number: PCT/FR2001/000190
Authority: WO
Inventors: Marc Cantegril
Original assignee: Thide Environnement
Priority date: 2000-01-21
Filing date: 2001-01-19
Publication date: 2001-07-26
Also published as: FR2804043A1; FR2804043B1; EP1248671A1; AU2001235567A1

Abstract

The invention concerns a method for treating gases derived from thermolysis of industrial and/or household and/or biomass waste, and containing at least a condensable hydrocarbon comprising at least a step a) which consists in directly contacting the gas derived from thermolysis, with a flux of oils driven countercurrent to the gas to be treated and having a temperature gradient relative to the gas to be treated to provoke condensation of at least a liquid phase consisting essentially of condensable hydrocarbon and to obtain a treated gas depleted in condensable hydrocarbon, for utilisation for energy purposes.

Description

Process and installation for purifying gases from thermolysis of waste

The present invention relates to the field of the purification of gases resulting from thermolysis of waste, with a view in particular to the energy recovery of the gases thus purified.

The term “waste” is understood here to mean any solid or pasty product containing in particular organic matter and comprising, for example industrial or household waste or else products of biomass or the like.

Generally speaking, thermolysis applied to waste consists in decomposing it under the action of heat. This decomposition produces solids which are generally called carbon solids and which are treated for recycling and / or recovery. This decomposition also produces combustible gases which may contain pollutants which may be released into the environment after combustion.

The Applicant has posed the problem of purifying these gases resulting from thermolysis, with a view in particular to energy recovery from these purified gases.

The present invention provides a solution to this problem.

It therefore aims to propose a solution for purifying gases from thermolysis in order in particular to limit the use of smoke treatments made necessary by changes in regulations.

It also aims to prepare the gases in order to temporarily store them in a gasometer in order to make them usable in standard thermal machines running on natural gas. It also aims to energetically recover the gaseous compounds resulting from thermolysis, in particular for using them in gas burners, combustion chambers, boilers for producing steam or hot water, internal combustion engines, gas turbines, etc.

Thus, it relates to a process for treating gases from thermolysis of industrial and / or household waste and / or biomass, and containing at least one condensable hydrocarbon, characterized in that it comprises at least one step a) consisting in bringing the gas from the thermolysis into direct contact with an oil flow sent against the current of the gas to be treated and having a temperature gradient with respect to the gas to be treated to cause condensation of at least one liquid phase formed essentially of condensable hydrocarbons and thus obtain a treated gas depleted in condensable hydrocarbons, with a view to energy recovery from this purified gas.

Thanks to the invention, the liquid phase formed essentially of condensable hydrocarbon is able to be circulated again against the flow of the gas to be treated, or to be recovered to be used as thermolysis fuel or to be used as fuel from a heat engine running on condensable hydrocarbons.

Advantageously, the separation of the condensable hydrocarbons, for example heavy hydrocarbons of the heavy petrol, kerosene, diesel and other type, is carried out (for example at the start of the installation) by a flow of oil which is inexpensive from an economic point of view, by example of drain oil or the like.

In addition, the Applicant has observed that by proceeding first with the separation of the hydrocarbons, the purification treatment of the gas resulting from the thermolysis makes it possible not only to recycle these hydrocarbons but also to improve the purification cycle of this gas, in particular by limiting pollution of washing water by hydrocarbons and / or oils. Preferably, the method further comprises a step b) which consists in bringing the treated gas depleted in condersable hydrocarbons into direct contact with pressurized water having a temperature gradient with respect to the gas to be treated to cause condensation. of a liquid fraction containing essentially water and soluble acid gases and thus obtaining a treated gas further depleted in acid gases and water vapor.

Preferably, the method further comprises a step c) consisting in storing the treated gas thus obtained for use as fuel in thermal machines operating on gas.

Advantageously, before step a) step i) consists in injecting into the gases from the thermolysis a basic reagent or a mixture of reagents in order to neutralize the acid gases.

Advantageously, between step i) and step a), there is further provided a step ii) consisting in capturing the solid particles resulting from the neutralization of the acid gases as well as the solid particles contained in the gas resulting from the thermolysis. .

Before storage, that is to say before step c), it is possible to add a step iii) consisting in washing the treated gas depleted in condensable hydrocarbons and in acid gases with water under pressure and having a gradient of temperature relative to the gas to be treated in order to cause the condensation of a liquid fraction containing essentially water and dissolved carbon dioxide and to obtain a treated gas further depleted in carbon dioxide.

Preferably, the liquid fraction containing essentially water and soluble acid gases is evacuated in a reserve cooled by a water exchanger in order to recirculate the water against the flow of the gas to be treated and to separate the acid gases by desorption at atmospheric pressure. Likewise, the liquid fraction essentially containing water and dissolved carbon dioxide is evacuated into a reserve cooled by a water exchanger in order to recirculate the water against the flow of the gas to be treated and to separate the carbon dioxide.

In practice, step c) of storage is supplemented by a step d) of purging the water accumulated during storage.

The present invention also relates to a device for treating gases resulting from thermolysis of industrial and / or household waste and / or biomass for the implementation of the process claimed above.

Other characteristics and advantages of the invention will become apparent in the light of the detailed description below and of the drawings in which:

FIG. 1 is a general view of the process for purifying gases from thermolysis according to the invention, and

- Figure 2 is a flowchart illustrating the steps of the method according to the invention.

The designs contain elements of a certain character. As such, they will be used to describe the invention and, if necessary, to define it.

With reference to FIG. 1, the installation comprises a thermolysis furnace 1 comprising an inlet interface 3 for receiving the waste to be treated and an outlet interface 5 for discharging the waste treated by thermolysis.

The output interface 5 includes an output 7 connected to a station for recovering carbonaceous solids 9. The carbonaceous solids are intended to be treated in order to be recovered and recovered as fuel, for example. The treatment comprises several stages, in particular stages of washing, separation, decantation, rinsing in order to rid the carbonaceous solid materials of the pollutants fixed on the particles of said materials.

The outlet interface 5 also includes an outlet 11 for removing the gases from the thermolysis of the waste.

The gases from the thermolysis are extracted through a line 13 located, for example, in the upper part of the thermolysis oven 1.

Absorbents or reagents are contained, for example in a storage hopper 15 equipped with a sealed reservoir and with a means for controlling the dosing of the reagent, such as a screw doser 17 or a rotary valve or the like, driven by a variable speed electric motor.

The pipe 13 has a geometry and a length making it possible to ensure sufficient contact time for the neutralization of the acid gases.

The reagent or mixture of reagents delivered by the hopper 15 and the control valve 17 is injected into the gases in powder form. A line 21 connects the hopper 15 to a point 19 of the line 13.

The hopper 15 has the function of storing the reagent for neutralizing the acid gases contained in the thermolysis gases. These acid gases, in particular Hcl, are capable of contributing, during the cooling of the combustion fumes produced by a burner, to the production of dangerous compounds of the dioxin and furan type.

The elimination or more precisely the neutralization of acid gases is also made necessary when it is desired to use the gas resulting from thermolysis in a thermal machine, engine or gas turbine.

The reagent used is a basic and hot powder, such as calcium hydroxide, calcium bicarbonate or the like, whose mixture with thermolysis gases in turbulent regime leads to an intimate gas / solid contact favorable to the neutralization of gases of the Hcl, H ₂ S, S0 ₃ , S0 ₂ and others types.

The flow rate of the reagent delivered in the gas line is regulated by measurements made continuously on the gases leaving the dust collector which will be described in more detail below.

Line 13 is advantageously maintained over its entire length at a temperature slightly higher than that of the gases at the outlet of the thermolysis oven, for example using electric tracing or using steam, to avoid condensation of the hydrocarbon vapors which can impede the circulation of the mixture.

Line 13 can be fitted with a chosen device (not shown) so as to facilitate and optimize the mixing of the absorbent and the hot gases. The hot thermolysis gases treated and cleaned up in line 13 can then be separated from the absorbent.

For this, the pipe 13 opens into a gas / solid separator 23, for example a cyclone or a set of several cyclones arranged in series and / or in parallel.

Preferably, the gas / solid separator 23 consists of a dedusting mechanism which has the function not only of capturing the dust contained in the thermolysis gases but also of capturing the absorbent or reagent entrained by the gas flow.

The dust removal mechanism 23 consists of at least one soulless screw placed in a horizontal pipe maintained at temperature by electrical tracing or by heating the pipe in a smoke flue.

Periodically, the dust removal screw 25 is rotated and the trapped dust is returned by gravity in theimolysis furnace via a line 27 connecting the dedusting mechanism 23 to the outlet interface 5. The salts from the gas neutralization reactions are mixed with the carbonaceous solid materials produced by thermolysis and treated in the equipment 9 provided for this effect.

Preferably, the dedusting mechanism comprises two dedusting assemblies (for example screws) arranged in parallel to allow alternating the cleaning sequences of the pipes without disturbing the flow of gases and thus ensuring the possibility of continuous operation of the thermolysis installation.

The quality of the acid gases as well as the absorbents or reactants which have reacted can be checked online. Such an analysis makes it possible, for example, to determine the quantity of reagents to be added according to the nature of the acid gases and / or to decide on the possibility of recycling or not the absorbent or reagent.

According to the invention, the outlet 29 of the dedusting mechanism 23 advantageously opens into a condenser 31 to bring the hot gases coming from thermolysis into direct contact with a flow of oil sent against the current of the gas to be treated and having a gradient of temperature with respect to the gas to be treated to cause the condensation of at least one liquid phase formed essentially of condensable hydrocarbons and thus obtain a treated gas depleted in condensable hydrocarbons.

In practice, the condenser 31 consists of a packed column 33 sprinkled continuously from the top 35 with a flow of cooled oil. The oils circulate against the flow of hot gases in the packing mass and heat up in contact with the gases. The gases are cooled and part of the hydrocarbons condense. These condensable hydrocarbons are then entrained by the liquid flow which is recovered in lower part 37 of the column and directed towards a storage tank 39 cooled by a water circuit 41.

The temperature of the tarpaulin oils is adjusted according to the characteristics of the oily condensates, for example 10 ° C. above the fluidity temperature.

The excess condensed oil flow is periodically extracted from the tank 39 and directed to a storage 43 before evacuation or internal recovery 45, that is to say recovered to be used as fuel for thermolysis or to be used as an oxidizer for a thermal machine operating on condensable hydrocarbons.

For example, the temperature of the oil flow in the upper part 35 of the column before being brought into contact with the gas to be treated is of the order of 80 ° C.

The temperature of the hot gases from the thermolysis at outlet 29 of the dust removal mechanism before contacting with the oil flow is of the order of 350 ° C.

In the lower part 37, the temperature of the liquid phase formed essentially of condensable hydrocarbons after bringing the oil flow into contact is of the order of 150 ° C.

The term “oil flow” is understood here to mean any flow of mineral or organic component having an oily consistency and advantageously having combustible characteristics.

For example, at the start of the installation, the oil flow consists of drain oil or "FOD N ° 2" type oil (for "fuel oil domestic"). Then, during treatment, the oil flow can consist of condensable hydrocarbons from the oil / gas separation according to the invention. The oil flow is circulated by a pump 47 disposed between the lower part of the tank 39 and the upper part 35 of the column 31.

The treated gas depleted in condensable hydrocarbons is extracted from column 31 by a pipe 49.

Advantageously, the pipe 49 opens into a condenser or washer 51 to bring the hydrocarbon-depleted gas into direct contact with pressurized water in order to wash this gas and to further eliminate the acid gases.

In practice, this contacting is carried out using a water ejector 55 in an enclosure 51. The ejector 55 is supplied by a pipe 57 from a reserve tank 59 by a flow pump 61 and variable pressure.

The thermolysis gases from line 49 are sucked in and cooled by the flow of water coming from line 57. The traces of residual acid gases are dissolved in the liquid which is continuously discharged towards the reserve tank 59 cooled by a water exchanger 63.

Advantageously, a metering pump 53, regulated by a pH sensor, maintains the waters of the tank 59 at a basic pH value by injection of basic reagent. The condensed water surpluses are continuously evacuated via a pipe 65 to the washing 9 of the carbonaceous solids of the thermolysis installation by the pump 61.

The treated gas depleted in condensable hydrocarbons and in acid gases is extracted from the condenser 51 by a pipe 67.

Advantageously, the pipe 67 opens into a condenser or washer 69 in order to bring the gas depleted in hydrocarbon and acid gases into direct contact with water under pressure in order to wash this gas and also eliminate carbon dioxide. This washing step consists in washing the treated gas depleted in condensable hydrocarbons and in acid gases with water under pressure and having a temperature gradient with respect to the treated gas to cause the condensation of a liquid fraction essentially containing water and carbon dioxide and thus obtain a treated gas further depleted in carbon dioxide C0 ₂ .

In practice, the gas washer 69 consists of an enclosure 71 under pressure composed of a reservoir and a water ejector 73 supplied from a reserve tank 75 by a pump 77 with variable flow and pressure.

The thermolysis gases from line 67 are sucked in by the flow of pressurized water routed through line 79 connecting the tank 75 to the ejector 73.

Part of the soluble gases, essentially consisting of carbon dioxide, is dissolved in the liquid which is then removed under pressure and continuously to the reserve tank 75.

The fraction of insoluble gas constitutes the purified combustible gas with high calorific value. This gas is extracted from the washer 69 through a pipe 81.

The flow of liquid 83 coming from the washer 69 and containing the gases in solution is expanded 85 to atmospheric pressure and purged 87 with the compressed air of the residual gases.

The excess condensed water is periodically removed via a pipe 89 to the rinse 9 of the carbonaceous solids of the thermolysis installation.

Advantageously, the storage of the purified gases and coming from the pipe 81 comprises a step of purging the water accumulated during the storage. This purge consists of an enclosure 91 for relaxing the thermolysis gases. The condensate trap works on the cooling / expansion principle. Its function is to reduce the pressure of the purified gases to a value compatible with the storage system.

For example, the pressure of the purified and stored gases is of the order of 8 bars while the pressure at the outlet of the gas washer 69 is of the order of 15 bars. The expansion of the gases causes the residual water vapor to cool and condense. This residual water vapor is evacuated via line 93 to the rinsing station 9 for the carbonaceous solids of the thermolysis installation.

Storage is carried out using a gasometer 95 which may be of the flexible type for low pressure applications or of the rigid type for medium pressure applications.

Regulation of gas treatment is ensured by adjusting certain parameters, in particular the flow rate of the water circulation pumps in the ejectors as well as the gas pressure in the tanks.

The regulation is ensured by a computerized system centralizing the information from sensors of different physical quantities such as gas pressure, gas temperature, carbon dioxide content of the purified gas, pH of the tarpaulin water, level of the oil and water, gasometer filling level, cooling water flow, and cooling water inlet and outlet temperature.

The installation according to the invention can also be completed by a condenser with tubular bundles (indirect) placed after the packed condenser (direct). This indirect condenser makes it possible to capture a light fraction of condensable hydrocarbons. The fluid used in the bundle is water or an oil suitable for the condensation function. The water heated in the tube bundle condenser is cooled by exchanger and recirculated. Thanks to the invention, the raw thermolysis gas is purified in the following proportions by mass.

According to the invention, the water content can go from 30 to 50% to 0.

In carbon dioxide, the proportion is reduced from 30 to 35% to 15% at most according to the invention.

Gases with significant calorific value, such as gases in CO, H ₂ , CH ₄ , C ₂ H ₄ , C ₂ H ₆ , C ₃ + are advantageously recovered and stored according to the invention.

On the other hand, the condensable hydrocarbons (at room temperature) are eliminated, as are the components Hcl, H ₂ S and S0 ₂ .

With reference to FIG. 2, the various stages of the treatment of gases from thermolysis have been summarized, in the form of a flowchart.

Step a) of gas / hydrocarbon separation is very advantageous since it avoids the dissolution of hydrocarbons (phenol for example) which are very difficult and costly to separate from water.

Step b) of neutralization of the acids after separation of the hydrocarbons is useful because it makes it possible to eliminate polluting and corrosive gases.

Stage c) of storage, preferably accompanied by the stage of purge d), aims to achieve an energy recovery of the purified gases under good conditions.

Stage i) of neutralization of the acid gases before separation of the hydrocarbons and stage ii) of dedusting, aim to significantly improve the purification of the gases resulting from thermolysis. Likewise, step iii) of washing carbon dioxide gases advantageously contributes to the elimination of inert gases and thus reduces the necessary storage capacities.

Furthermore, it should be noted that the water used in the purification of gases is recovered according to the invention in the treatment station for carbonaceous solids, so as to also be treated in a closed circuit, which eliminates the release of water. worn out.

Claims

claims

1. Process for the treatment of gases from thermolysis of industrial and / or household waste and / or biomass, and containing at least one condensable hydrocarbon, characterized in that it comprises at least one step a) consisting in bringing into direct contact the gas coming from thermolysis, with a flow of oils sent against the current of the gas to be treated and having a temperature gradient with respect to the gas to be treated to cause the condensation of at least one liquid phase formed essentially of hydrocarbon condensable and thus obtain a treated gas depleted in condensable hydrocarbon, for energy recovery of said purified gas.

2. Method according to claim 1, characterized in that it further comprises a step b) which consists in bringing into direct contact the treated gas depleted in condensable hydrocarbon with water under pressure and having a temperature gradient with respect to to the gas to be treated in order to cause the condensation of a liquid fraction essentially containing water and soluble acid gases and to obtain a treated gas depleted in addition of acid gas.

3. Method according to claim 1 or claim 2, characterized in that it further comprises a step c) consisting in storing the treated gas thus obtained for use as an oxidant in thermal machines operating on gas .

4. Method according to claim 1, characterized in that it comprises, before step a) a step i) consisting in injecting into the gas resulting from the thermolysis a reagent or a mixture of reagents in order to neutralize the acid gases.

5. Method according to claim 4, characterized in that between step i) and step a), there is further provided a step ii) of dusting consisting in capturing the solid particles resulting from the neutralization of the acid gases thus than the solid particles contained in the gas from thermolysis.

6. Method according to claims 1 to 3, characterized in that it further comprises, between step b) and step c), a step iii) consisting of washing the treated gas depleted in condensable hydrocarbon and gas acid with water under pressure and having a temperature gradient with respect to the treated gas to cause the condensation of a liquid fraction containing essentially water and dissolved C0 ₂ and to obtain a treated gas depleted in addition of C0 ₂ .

7. Method according to claim 1, characterized in that the liquid phase formed essentially of condensable hydrocarbon is able to be recirculated against the current of the gas to be treated, or to be recovered to be used as fuel for thermolysis or to be used as fuel for a thermal machine operating on condensable hydrocarbons.

8. Method according to claim 1, characterized in that the liquid fraction containing essentially water and soluble acid gases is evacuated in a reserve cooled by a water exchanger in order to recirculate the water against the current of the gas to treated and neutralize the dissolved acid gases.

9. Method according to claim 1, characterized in that step c) of storage further comprises a step d) of purging the water accumulated during storage.

10. Method according to claim 4, characterized in that the liquid fraction essentially containing water and dissolved CO is discharged into a reserve cooled by a water exchanger in order to recirculate the water against the flow of the gas to be treated and to separate the C0 ₂ .

11. Device for treating gas from thermolysis of industrial and / or household waste and / or biomass, and 1 D containing at least one condensable hydrocarbon, characterized in that it comprises at least one packed column (31) for bringing the gas coming from thermolysis into direct contact, with a flow of oils sent against the current of the gas treated and having a temperature gradient with respect to the gas to be treated to cause the condensation of at least one liquid phase formed essentially of condensable hydrocarbon and to obtain a treated gas depleted in condensable hydrocarbon, with a view to energy recovery of said gas sleek.

12. Device according to claim 11, characterized in that it further comprises a washing device (51, 55) for bringing into direct contact the treated gas depleted in condensable hydrocarbon with water under pressure and having a gradient of temperature with respect to the gas to be treated to cause the condensation of a liquid fraction containing essentially water and soluble acid gases and to obtain a treated gas depleted in acid gas.

13. Device according to claim 11, characterized in that it further comprises storage means (95) for storing the treated gas thus obtained for use as an oxidant in thermal machines operating on gas .

14. Device according to claim 11, characterized in that it further comprises an injection hopper (15) suitable for injecting into the gas resulting from thermolysis a reagent or a mixture of reagents in order to neutralize the acid gases.

15. Device according to claim 14, characterized in that it comprises a soulless screw (25) placed on the path of the gases resulting from thermolysis after neutralization of the acids and control means suitable for moving the screw on command in order to capture solid particles.

16. Device according to claim 11, characterized in that it further comprises a washing device (69) suitable for washing the treated gas depleted in condensable hydrocarbon and in acid gas with water under pressure and having a temperature gradient with respect to the gas to be treated to cause the condensation of a liquid fraction containing essentially water and C0 ₂ dissolved and obtain a treated gas depleted in addition of C0 ₂ .

17. Device according to claim 13, characterized in that the storage means comprise a device for purging (91) of the water accumulated during storage.

18. Device according to claim 16, characterized in that it comprises a reserve (39) suitable for receiving the liquid fraction containing essentially water and soluble acid gases, said reserve (39) being cooled by a heat exchanger water (41) in order to recirculate the water against the current of the gas to be treated and being equipped with separating means for separating the soluble acid gases.

19. Device according to claim 16, characterized in that it comprises a reserve (75) suitable for receiving the liquid fraction containing essentially water and dissolved C0 ₂ , said reserve being cooled by a water exchanger in order to recirculate the water against the current of the treated gas and being equipped with separating means to separate the C0 ₂ .