FR2804043A1 - Gas treatment for gas produced by thermolysis of waste comprises oil counterflow to condense hydrocarbon - Google Patents

Abstract

Gas treatment comprises subjecting the gas produced by thermolysis to direct contact by counterflow of oils at a temperature causing at least one hydrocarbon to condense into a liquid phase, creating a gas with a low hydrocarbon content that can be used as an energy source or can be subjected to further treatment with water to remove acid gases. Preferred Features: The treated gases can be stored and used to power gas-fuelled devices. An Independent claim is also included for a plant used for gas treatment comprising a packed column (31) for subjecting the gas to a counter-current of oil, a scrubber (51, 55) for condensing acid gases with high-pressure water, and a storage tank (95). An additional scrubber (69) can be used to remove carbon dioxide.

Description

The present invention relates to the field of the purification of gases resulting from the thermolysis of waste, with a view to the purification of waste gases from waste thermolysis. in particular the energy recovery of the gases thus purified. The term "waste" here means any solid or pasty product containing in particular organic matter and comprising, for example, industrial or household waste or else biomass products or the like. In general, a thermolysis applied to waste consists in decomposing them under the action of heat. This decomposition produces solids which are generally called carbonaceous solids and which are treated for recycling and / or upgrading. This decomposition also produces combustible gases that may contain pollutants that can be released into the environment after combustion. The Applicant has posed the problem of purifying these gases from thermolysis, especially for energy recovery of 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 to limit the use of smoke treatments made necessary by the evolution of regulations. It also aims to prepare the gases to temporarily store them in a gas meter to make them usable in standard thermal machines running on natural gas. It also aims to energetically enhance the gaseous compounds resulting from thermolysis, in particular for use 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 gas resulting from the 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 of bringing the gas coming from the thermolysis into direct contact with an oil flow sent countercurrently to the gas to be treated and having a temperature gradient with respect to the gas to be treated in order to cause the condensation of at least one essentially formed liquid phase of condensable hydrocarbons and thereby obtain a treated gas depleted in condensable hydrocarbons. Thanks to the invention, the liquid phase consisting essentially of condensable hydrocarbon is able to be circulated again against the current of the gas to be treated, or recovered for use as fuel for thermolysis or used as a fuel of a thermal machine operating with condensable hydrocarbons.

Advantageously, the separation of condensable hydrocarbons, for example heavy hydrocarbons of heavy gasoline type, kerosene, gas oil and others, is carried out (for example at the start of the installation) by a cheap oil flow economically. , for example oil drain or the like. In addition, the Applicant has observed that, by first proceeding to the separation of 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 product. gas, in particular by limiting the pollution of washing water by hydrocarbons and / or oils. Preferably, the method further comprises a step b) which consists in bringing the depleted condensed hydrocarbons treated gas into direct contact with pressurized water having a temperature gradient with respect to the gas to be treated in order to cause the condensation of a liquid fraction containing essentially water and soluble acid gases and thereby obtain a treated gas further depleted in acidic gases and water vapor.

Preferably, the method further comprises a step c) of storing the treated gas thus obtained for use as a fuel in gas-fired thermal machines.

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

Advantageously, between step i) and step a), there is further provided a step ii) of capturing the solid particles resulting from the neutralization of the acid gases and 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) of washing the treated gas depleted in condensable hydrocarbons and acid gases 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 substantially water and dissolved carbon dioxide and obtain a treated gas further depleted in carbon dioxide.

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

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

The present invention also relates to a gas treatment device from thermolysis of industrial waste and / or household and / or biomass for the implementation of the method claimed above.

Other features and advantages of the invention will emerge in the light of the detailed description below and the drawings in which - FIG. 1 is a general view of the process for purifying gases resulting from thermolysis according to the invention, and FIG. 2 is a flowchart illustrating the steps of the method according to the invention.

The drawings include elements of a certain character. As such, they will be used to describe the invention, and if necessary to the definition thereof.

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 exit interface 5 for discharging the thermolysis treated waste.

The output interface 5 has an outlet 7 connected to a carbon solids recovery station 9. The carbonaceous solids are intended to be treated in order to be recovered and recovered as a fuel, for example. The treatment comprises several steps, including washing steps, separation, decantation, rinsing to rid the carbonaceous solids pollutants attached to the particles of said materials. The output interface 5 also includes an outlet 11 for evacuating the gases resulting from the thermolysis of the waste.

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

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

The pipe 13 has a geometry and a length makes it possible to ensure a sufficient contact time for 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 pipe 21 connects the hopper 15 to a point 19 of the pipe 13.

The purpose of the hopper 15 is to store the neutralization reagent for the acid gases contained in the thermolysis gases. These acid gases, in particular HCl, may contribute, during the cooling of combustion fumes produced by a burner, to the production of dangerous compounds of the dioxin and furan type.

The elimination or, more exactly, the neutralization of the acid gases is also 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 mixing with the turbulent thermolysis gases results in an intimate gas / solid contact favorable to the neutralization of the HCl-type gases. , H2S, SO3, SO2 and the like.

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

The pipe 13 is advantageously maintained over its entire length at a temperature slightly higher than that of the gases at the outlet of the thermolysis furnace, for example by means of electric tracing or by means of steam, in order to avoid the condensation of hydrocarbon vapors that may impede the circulation of the mixture.

The pipe 13 may be equipped with a chosen device (not shown) so as to facilitate and optimize the mixing of the absorbent and hot gases. The hot thermolysis gases treated and cleaned 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 whose function is not only the capture of the dust contained in the thermolysis gas but also the capture of the absorbent or reagent entrained by the gas flow.

The dedusting mechanism 23 consists of at least one coreless screw placed in a horizontal pipe maintained in temperature by electric tracing or by reheating the pipework in a smoke flue.

Periodically, the dust removal screw 25 is rotated and the trapped dust is returned by gravity into the thermolysis furnace via a pipe 27 connecting the dust removal mechanism 23 to the outlet interface 5. The salts resulting from the neutralization reactions of the The gases are mixed with the carbonaceous solids produced by the thermolysis and treated in the equipment 9 provided for this purpose.

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

A quality control of acid gases as well as reactive absorbents or reagents can be performed online. Such an analysis makes it possible, for example, to determine the quantity of reagents to be added depending on 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 opens advantageously in a condenser 31 to directly contact the hot gases from the thermolysis with an oil flow sent against the current of the gas to be treated and having a gradient temperature relative to the gas to be treated to cause the condensation of at least one liquid phase formed essentially of condensable hydrocarbons and thereby obtain a treated gas depleted condensable hydrocarbons.

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

The temperature of the oils of the tarpaulin is adjusted according to the characteristics of the oily condensates, for example 10 ° C above the flow 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 recovered for use as fuel for the thermolysis or to be used as the oxidant of a heat machine operating with condensable hydrocarbons.

For example, the temperature of the oil flow at the top of the column before contacting the gas to be treated is of the order of 80.degree.

The temperature of the hot gases resulting from the thermolysis at the outlet 29 of the dedusting mechanism before coming into contact with the oil flow is of the order of 350.degree.

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

Here, the term "oil flow" means 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 oil of oil or oil type "FOD N 2" (for "fuel oil domestic"). Then, during treatment, the oil flow may consist of condensable hydrocarbon res derived from the oil / gas separation according to the invention. The circulation of the oil flow is carried out 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 the column 31 by a pipe 49. Advantageously, the pipe 49 opens into a condenser or scrubber 51 to directly contact the hydrocarbon-depleted gas with pressurized water to wash this gas and further eliminate acid gases.

In practice, this contacting is performed using a water ejector 55 in a chamber 51. The ejector 55 is fed by a pipe 57 from a reserve tank 59 by a pump 61 to flow and variable pressure.

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

Advantageously, a metering pump 53, regulated by a pH sensor, maintains the water of the tank 59 at a basic pH value by injection of basic reagent. The condensed excess water is discharged continuously via a pipe 65 to the washing 9 of the carbon solids of the thermolysis plant by the pump 61.

The treated gas depleted of condensable hydrocarbons and acid gases is extracted from the condenser 51 via a pipe 67. Advantageously, the pipe 67 opens into a condenser or scrubber 69 for direct contacting the depleted gas with hydrocarbons and acid gases with carbon dioxide. pressurized water in order to wash this gas and further eliminate the carbonaceous gases. This washing step consists of washing the treated gas depleted of condensable hydrocarbons and acid gases with pressurized water and having a temperature gradient with respect to the treated gas to cause the condensation of a liquid fraction essentially containing water. water and carbon dioxide and thus obtain a treated gas further depleted in CO2 gas.

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

The thermolysis gases coming from the pipe 67 are sucked by the flow of pressurized water conveyed by the pipe 79 connecting the tank 75 to the ejector 73.

A portion of the soluble gases, consisting essentially of carbonaceous gases, is dissolved in the liquid which is then discharged under pressure and continuously to the reserve tank 75.

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

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

Condensed excess water is discharged periodically via line 89 to the flushing 9 of the carbon solids of the thermolysis plant.

Advantageously, the storage of purified gases and from line 81 comprises a step of purging water accumulated during storage. This purge consists of an enclosure 91 for relaxing the thermolysis gases. The condensate trap operates on the principle of cooling / expansion. 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 scrubbed and stored gases is of the order of 8 bars while the outlet pressure of the gas scrubber 69 is of the order of 15 bars. The expansion of the gases causes cooling and condensation of the residual water vapor. This residual water vapor is discharged via line 93 to the flushing station 9 of the carbon solids of the thermolysis plant.

The storage is performed using a gasometer 95 which can be flexible type for low pressure applications or rigid type for medium pressure applications.

The regulation of the 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 sensor information of the different physical quantities such as gas pressure, gas temperature, carbon dioxide content of the purified gas, tarpaulin water pH, oil and water tarpaulins level. , fill level of the gasometer, flow of cooling water, and inlet and outlet temperature of the cooling water.

The installation according to the invention can also be completed by a tubular bundle condenser (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 beam is water or oil adapted to the function of condensation. The heated water in the tube bundle condenser is cooled by exchanger and recirculated. Thanks to the invention, the raw gas of thermolysis is purified in the following proportions by mass.

The water content can pass according to the invention, 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.

The gases with a large calorific value, such as the gases CO, H2, CH4, C2H4, C2H6, C3 +, are advantageously recovered and stored according to the invention.

On the other hand, condensable hydrocarbons (at ambient temperature) are eliminated, as are the components Hcl, H2S and SO2.

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

Step a) gas / hydrocarbon separation is very advantageous because it avoids the dissolution of hydrocarbons (phenol for example) very difficult and expensive to separate water.

Step b) acid neutralization after separation of hydrocarbons is useful because it eliminates polluting and corrosive gases.

The storage step c), preferably accompanied by the purge step d), aims at achieving energy recovery of the purified gases under good conditions.

The step i) of acid gas neutralization before separation of the hydrocarbons and the step ii) of dedusting, aim at significantly improving the purification of the gases resulting from the thermolysis.

 Similarly, step iii) of washing the carbon gases advantageously concurs in the elimination of inert gases and thus reduces the storage capacity required.

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

Claims (19)

<U> Claims </ U> 1. Process for the treatment of gases resulting from the 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) of putting in direct contact the gas resulting from the thermolysis, with a flow of oils counter-currently flow of the treated gas 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 thereby obtain a treated gas depleted of condensable hydrocarbon. 2. Method according to claim 1, characterized in that it further comprises a step b) which consists in bringing the treated gas depleted in condensable hydrocarbon into direct contact with water under pressure and having a temperature gradient relative to the gas to be treated to cause the condensation of a liquid fraction containing essentially water and soluble acid gases and obtain a treated gas further depleted in acid gas. 3. Method according to claim 1 or claim 2, characterized in that it further comprises a step c) of storing the treated gas thus obtained for use as an oxidizer in thermal machines operating at gas. 4. Method according to claim 1, characterized in that it comprises before step a) a step i) of injecting into the gas from the thermolysis reagent or a mixture of reagents to neutralize the acid gas. 5. Method according to claim 4, characterized in that between step i) and step a), is further provided a step ii) dedusting consisting of capturing the solid particles resulting from the neutralization of acid gases and than the solid particles contained in the gas resulting from the thermolysis. 6. Method according to claims 1 to 3, characterized in that it further comprises, between step b) and step c), a step iii) of washing the treated gas depleted in condensable hydrocarbon and gas acid with pressurized water and having a temperature gradient with respect to the treated gas to cause the condensation of a liquid fraction containing substantially water and dissolved CO 2 and to obtain a treated gas further depleted in CO 2 7. Method according to claim 1, characterized in that the liquid phase consisting essentially of condensable hydrocarbon is adapted to be recirculated against the current of the treated gas, or to be recovered for use as fuel for the thermolysis or to be used as a fuel of a heat 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 discharged into a reserve cooled by a water exchanger in order to recirculate the water against the flow of gas. treated and neutralize the dissolved acid gases. 9. The method of claim 1, characterized in that the storage step c) further comprises a step d) of purging the water accumulated during storage. 10. Process according to claim 4, characterized in that the liquid fraction containing essentially water and dissolved CO 2 is discharged into a reserve cooled by a water exchanger in order to recirculate the water against the stream of the treated gas. and to separate the CO 2. 11. A device for treating gas resulting from the 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 packed column (31) to implement direct contact with the gas from the thermolysis, with a flow of oils counter-currently flow of the treated gas 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 obtain a treated gas depleted in condensable hydrocarbon. 12. Device according to claim 11, characterized in that it further comprises a washing device (51, 55) for putting in 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 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 gas-fired thermal machines. 14. Device according to claim 11, characterized in that it further comprises an injection hopper (15) adapted to inject into the gas from the thermolysis reagent or a mixture of reagents to neutralize the acid gases. 15. Device according to claim 14, characterized in that it comprises a screw without core (25) placed on the path of the gases from the thermolysis after neutralization of the acids and control means adapted to move on command the screw in order to capture the solid particles. 16. Device according to claim 11, characterized in that it further comprises a scrubber device (69) suitable for washing the treated gas depleted in condensable hydrocarbon and 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 substantially water and dissolved CO 2 and to obtain a further reduced CO 2 treated gas. 17. Device according to claim 13, characterized in that the storage means comprise a purge device (91) of water accumulated during storage. 18. Device according to claim 16, characterized in that it comprises a reserve (39) adapted to receive the liquid fraction containing essentially water and soluble acid gases, said reserve (39) being cooled by a heat exchanger. water (41) for recirculating the water against the stream of the treated gas 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) adapted to receive the liquid fraction containing essentially water and dissolved CO2, said reserve being cooled by a water exchanger to recirculate countercurrent water of the treated gas and being equipped with separating means for separating the CO 2.