FR3146313A1 - Plant and process for producing carbon dioxide and energy from biomass - Google Patents

Abstract

The invention relates to an installation (1) for producing carbon dioxide (CO2) and energy from biomass comprising successively: - a biomass gasifier (12), - a burner (13) connected to the outlet of the gasifier (12) for the combustion of the synthesis gas resulting from the gasification of biomass, - a condensation boiler (15) connected to the outlet of the burner (13) for, on the one hand, cooling the combustion fumes coming from the burner (13) and comprising in particular carbon dioxide (CO2) and water vapor, and on the other hand condensing the water vapor contained in these combustion fumes, - a condenser (16) connected to the outlet of the condensation boiler (15) for further cooling the combustion fumes coming from the condensation boiler (15), and separating the water vapor and the carbon dioxide (CO2) from these fumes, and - means for recovering the carbon dioxide (CO2) separated from the water vapor in the condenser (16) and storage and/or distribution of this recovered carbon dioxide (CO2) to one or more cultivation greenhouses, the installation (1) further comprising at the outlet of the gasifier (12) means for generating heat and/or electricity (14) from the synthesis gas resulting from the gasification of biomass. [Fig 1]

Description

Plant and process for producing carbon dioxide and energy from biomass 1. Field of the invention

The present invention relates to an installation and a method for producing carbon dioxide energy from biomass. The present invention relates more particularly to an installation and a method for gasifying biomass to extract a synthesis gas therefrom so as to produce carbon dioxide and energy.

2. Prior art

A practice of the greenhouse profession, particularly tomato growers, consists of heating greenhouses and increasing the concentration of carbon dioxide ( _CO2 ) in the air to promote plant growth. Carbon dioxide ( _CO2 ) is essential for the phenomenon of photosynthesis and an enrichment in _CO2 mainly helps to increase crop yields. However, this practice is in contradiction with the objectives mentioned above because this _CO2 is generally produced from natural gas and propane, the two fuels most frequently used in greenhouse farming.

Many fuels can be used to produce energy, such as heat and electricity. In times of climate emergency, renewable energy sources such as biomass are increasingly important because they are more environmentally friendly.

Furthermore, greenhouse growers pay particular attention to energy savings since it is their second largest expense after labor. This has led many greenhouse growers to turn to alternative fuels, particularly biomass, for heating greenhouses.

The aim of the present invention is to propose a new installation and a new process, which make it possible to produce energy and _CO2 (for greenhouses for example), in an optimized manner from biomass.

3. Presentation of the invention

To do this, the invention proposes an installation for producing carbon dioxide ( _CO2 ) and energy from biomass comprising successively:

- a biomass gasifier,

- a burner connected to the gasifier outlet for the combustion of synthesis gas from biomass gasification,

- a condensing boiler connected to the burner outlet to, on the one hand, cool the combustion fumes coming from the burner, including in particular carbon dioxide ( _CO2 ) and water vapor, and on the other hand, condense the water vapor contained in the combustion fumes,

- a condenser connected to the outlet of the condensing boiler to further cool the combustion fumes from the condensing boiler, and separate the water vapor and carbon dioxide ( _CO2 ) from these fumes, and

- means for recovering carbon dioxide ( _CO2 ) separated from the water vapor in the condenser and means for storing and/or distributing this recovered carbon dioxide ( _CO2 ) to one or more cultivation greenhouses,

the installation further comprising, at the outlet of the gasifier, means for generating heat and/or electricity from the synthesis gas resulting from the gasification of biomass.

The idea therefore germinated among inventors to produce renewable carbon dioxide ( _CO2 ) from the gasification and combustion of biomass, and to use this carbon dioxide ( _CO2 ) to supply greenhouses in particular.

The inventors have thus developed a fixed bed gasification unit (gas boiler), used for the conversion of solid organic matter (also called biomass) into synthesis gas, this gasification unit being associated with a synthesis gas combustion burner successively connected to a condensation boiler and a smoke dehumidification condenser so as to recover the carbon dioxide ( _CO2 ) from the combustion fumes.

This carbon dioxide ( _CO2 ) can be injected into the greenhouse for plant photosynthesis and/or stored.

At the same time, the installation allows the cogeneration of electricity and/or heat from the synthesis gas produced during gasification.

The installation of the invention makes it possible to recover biomass and in particular agricultural by-products or waste, such as wood chips or pellets, sawdust, crushed wooden pallets, or any other organic matter (sludge, agricultural by-products, etc.), not only to produce energy, as is commonly done with a view to sustainable development, but also to produce carbon dioxide, where carbon dioxide is usually produced from fossil energy sources such as natural gas.

According to a particular aspect of the invention, the installation further comprises means for treatment by filtration of the synthesis gas resulting from the gasification of biomass in the gasifier before its injection into the burner.

According to a particular aspect of the invention, the means for generating heat and/or electricity comprise an electric generator supplied with synthesis gas from the gasification of biomass.

According to a particular aspect of the invention, the installation further comprises means adapted to evacuate part of the ash of carbonaceous material resulting from the gasification in the gasifier.

According to a particular aspect of the invention, the gasifier is of the co-current fixed bed type.

According to a particular aspect of the invention, the installation comprises means for pre-treating the biomass by drying before introducing the biomass into the gasifier.

The invention also relates to a method for producing carbon dioxide and energy from biomass using the installation as described above, in which:

- biomass is introduced into the gasifier,

- the synthesis gas is evacuated from the gasifier to introduce it partly into the burner adapted for the combustion of synthesis gas and partly into the means of generating heat and/or electricity,

- the fumes from combustion are treated in a condensation boiler then a condenser to extract carbon dioxide ( _CO2 ) and distribute it to one or more greenhouses.

4. Description of figures

Other characteristics and advantages of the invention will appear on reading the following description of a particular embodiment, given as a simple illustrative and non-limiting example, and the appended drawings among which:

is a schematic view of a plant for producing carbon dioxide and energy from biomass according to one embodiment of the invention,

is a schematic view of a gasifier that can be implemented in the installation of the invention.

5. Detailed description of an embodiment of the invention

There schematically represents an installation 1 for producing carbon dioxide and energy from biomass according to one embodiment of the invention.

This installation 1 comprises an automatic feed unit 11 of a biomass gasifier 12. The gasifier 12 is associated on the one hand with a burner 13 and on the other hand with a generator set 14. The outlet of the burner 13 is connected to a condensing boiler 15, itself connected to a dehumidification unit for the fumes from the boiler 15 taking the form of a condenser 16. The carbon dioxide (CO ₂ ) extracted from the condenser 16 is stored and/or conveyed by PVC pipes to one or more growing greenhouses, for example.

Installation 1 also includes a UF filtration treatment unit for the hot synthesis gas from gasifier 12 before its injection into burner 13.

The structure of such an installation 1 and the main stages of production of CO ₂ and energy from biomass are detailed below in relation to the .

Step 1 – Biomass gasification

The biomass, which is used as fuel, is introduced into the gasifier, or gas boiler, 12 through an inlet pipe and a conveyor.

Biomass is defined as solid organic matter, such as wood waste in various forms (chips, pellets, shredded wood, etc.). In the example described here, it is coarse, dry wood in the form of wood chips. This type of waste has the advantage of being inexpensive.

A pre-treatment of the biomass corresponding to a drying phase can be implemented before the introduction of the biomass into the gasifier 12. This upstream drying, which is optional, aims to reduce the humidity level in the wood which is generally between 40 and 50% at the start. The humidity level targeted after drying is less than 20%, preferably between 15 and 20%, and preferably less than 15%.

It should be noted that the humidity of the carbon resource produces water vapor which participates in the gasification process.

The pre-dried or non-pre-dried biomass is therefore injected into the gasification unit or gasifier 12, the operating conditions of which are typically a pressure P of approximately 0.01 bar) and a temperature T of approximately 400°C depending on the fuel used. This results in the production of a gas mixture, called synthesis gas, comprising CO, H2, CO2, CH4, O2 and N2.

The gasifier 12 is here of the co-current fixed bed reactor type with a thermal capacity or power of between 2000 and 3000 kWth (i.e. between 2 and 3 MWth).

It has a generally cylindrical shape. As is known, within the reactor, gasification converts all of the solid (biomass) into combustible gas and ash, the only discharge from the first stage.

It should be remembered that gasification generally consists of a thermal transformation of a combustible solid (coal, coke, peat, wood, etc.) in the presence of a gaseous compound (O2, air, _CO2 , water vapor, etc.). The aim of this transformation is generally to convert the solid in order to obtain a combustible gas mixture. It is therefore distinguished from pyrolysis, a thermal operation carried out in the absence of gas reacting with the solid, and from combustion in which most of the carbon contained in the solid is transformed into _CO2 .

In the gasifier 12 shown schematically in the , the solid fuel (biomass in this case) is introduced through the upper part of the reactor while the oxidizing agent (air) required for gasification is introduced at mid-height to initiate combustion and provide heat to the entire reactor. Due to this arrangement, the gas generated during gasification is evacuated from the reactor near the hottest zone and therefore has a relatively low tar content. Thus, the gradual increase in temperature makes it possible to obtain the various reactions driving the gases produced towards the hottest zone of the reactor. We can distinguish on the the three reaction zones of pyrolysis, oxidation and reduction, the ash accumulating in the lower part of the reactor.

The gasification of biomass in the gasifier 12 therefore consists of decomposing carbonaceous materials, here wood, in the presence of a reactive gas (air in this example), in order to obtain a combustible synthesis gas (often called “syngas” or “syngaz”), composed mainly of carbon monoxide (CO) and dihydrogen (H2).

This gasifier 12 also ensures effluent management via an ash recovery system comprising a system for removing char and ash with a water-cooled screw conveyor. It is indeed necessary for the proper running of the gasification process to evacuate the char particles which reduce the porosity of the reduction bed due to their small size. These ashes or biochar, recovered under the gasifier 12, are collected and evacuated via an automated system to a container (not shown).

Step 2 – Synthesis gas treatment

In the embodiment illustrated in the , a step of treating the hot synthesis gas coming from the gasifier 12, reaching a temperature of the order of 700°C, is implemented in a UF filtration treatment unit. The latter comprises a gas separation cyclone allowing the evacuation of coarse solid particles contained in the gas and a high-temperature bag filter or HTFE (for “ High-Temperature Filtering Equipment ” in English) allowing finer filtration of the gas.

Step 3 – Combustion

The gasifier 12 is associated with a burner 13 adapted to the combustion of the synthesis gas filtered by the UF filtration treatment unit.

In particular, once filtered, the synthesis gas (or “syngas”) obtained from the conversion of biomass in the gasifier 12 is burned in the combustion chamber of the burner 13, which is a dual-gas or dual-fuel burner.

The combustion fumes leaving the burner 13, including in particular carbon dioxide ( _CO2 ) and water vapor, are then directed to a condensing boiler 15, called a high-efficiency gas boiler. These fumes typically have a temperature of 150°C.

Step 4 – Condensing boiler (high efficiency)

The condensing boiler 15, called a high-efficiency gas boiler, comprises, in a known manner, a combustion chamber equipped with a burner in which the combustion fumes burn. An outer casing surrounds the combustion chamber at a distance so as to define a space filled with a liquid, water in this case, which heats up on contact with the heat exchange surface constituted by the wall of the combustion chamber.

In this condensing boiler 15, the water vapor contained in the combustion fumes from the burner 13 is condensed. By condensing, the water vapor from the combustion fumes releases heat or calories to heat the return water from the boiler heating circuit to a temperature of 90°C. At the same time, the cooled fumes are directed to a fume dehumidification unit or condenser 16 and the condensation water is discharged.

Condensing boilers are interesting for several reasons. First, they allow you to increase thermal efficiency by at least 10% and thus achieve significant savings. In addition, the combustion gases and fumes exit through the flue, cooled and freed from a large part of their humidity.

Step 5 – Condenser

The fumes from the condensing boiler 15 are then further dehumidified in a condenser (or fume dehumidification unit) 16 to separate the water and the carbon dioxide (CO ₂ ). Indeed, a certain amount of water in the form of condensation remains in the fumes leaving the boiler, even in the case of condensing boilers. The condensers are heat exchangers inside which a flow of cold water and a flow of hot gas (the fumes from the condensing boiler 15) meet, which, by crossing on either side of a wall, exchange their respective heat. In the condenser 16, the fumes cool until condensation by giving up their heat to the water in a heating system. Water at 40°C is thus recovered.

It can therefore be said that the condenser 16 completes the heat exchange work carried out in the condensing boiler 15 and allows the water vapour from the fumes to be condensed and the condensation heat to be recovered to heat the water returned from the heating system.

The condensing boiler 15 and the condenser 16 through which the combustion fumes pass successively make it possible to cool these fumes and to remove the humidity from these fumes. Thus, it has been found that 88% of the heat from the fumes can be recovered at the outlet of the condensing boiler 15 and that an additional 10% can be recovered in the condenser 16, which makes it possible to obtain optimum dehydration of the fumes.

It is indeed important that the temperature of the fumes circulating in the PVC pipes towards the greenhouses is not too high so as not to damage the pipes. It is also important that a minimum of humidity is injected into the greenhouses. The condensing boiler 15 and the condenser 16 make it possible to achieve these objectives, and in particular to cool the fumes at the outlet of the burner 13 which can reach a temperature of 150°C.

Step 6 – Storage and Diffusion of carbon dioxide (CO ₂ )

In this way, the carbon dioxide ( _CO2 ) present in the fumes is recovered and diffused into a greenhouse crop using a blower and PVC pipes. This carbon dioxide ( _CO2 ) can be filtered if necessary to be then diffused into a greenhouse or stored for uses other than enriching the carbon dioxide ( _CO2 ) content of the atmosphere of greenhouse crops.

Energy production

In the embodiment described here, the gasifier 12 is also associated with a specific generator set 14.

The filtered synthesis gas is thus also used to produce electricity and heat via the generator set 14. The latter comprises a gas engine and a generator to produce electricity, and is configured to also produce heat (thermal energy).

The syngas from gasification contains heat energy which can be converted into electrical energy by injecting it into the generator set 14. For example, 1 kg of biomass (wood) can produce between 1 and 1.3 kWh of electrical energy and between 1.7 and 2.5 kWh of thermal energy.

Syngas can more generally be injected into engines or turbines on which it acts in such a way as to produce electrical energy, directed towards the national grid for example.

Rather than a generator, any other thermal machine capable of converting the chemical energy from the combustion of the syngas produced in the gasifier into another form of energy of interest can be implemented.

Thus, in summary, in the present installation 1, the carbon from the wood is extracted by the gasifier so as to obtain a synthesis gas (CO/H2), possibly cleaned to remove fine particles, alkali metals, tars and others. This synthesis gas replaces fossil fuels to power a generator for the cogeneration of electricity and heat. This synthesis gas is also burned to produce pure carbon dioxide ( _CO2 ) extracted by condensation of the combustion fumes. This carbon dioxide ( _CO2 ) is injected into a greenhouse for photosynthesis in plants and/or stored for recovery on the market.

Automation and remote management of installation 1 are provided by a set comprising a device for measuring the humidity level of the biomass and a device for measuring humidity in the gas. This set supports the start-up of the installation, the management of the gasification reactor, the burner, the boiler and the condenser in particular.

Installation 1 can be used differently depending on the season or the time of day. During months without crops, it can be used only for electricity production, for example. For a first period of time during the day, it can be used to produce heat and carbon dioxide (CO ₂ ) (stored and recovered), and for a second period of time, it can be used to produce electricity only.

Other aspects and variants

The installation of the invention is particularly, but not exclusively, intended for greenhouse growers for the production of strawberries, cucumbers, aubergines or tomatoes, for example.

In this installation, other types of biomass, such as straw, cereals, fodder, wood chips or pellets, sawdust, crushed wooden pallets, or any other organic material (sludge, agricultural by-products, etc.), can be used as fuel.

The energy produced by the installation of the invention can be injected into the national network and the biochar (ashes) can be recovered.

Claims (7)

Installation (1) for the production of carbon dioxide ( _CO2 ) and energy from biomass comprising successively:
- a biomass gasifier (12),
- a burner (13) connected to the outlet of the gasifier (12) for the combustion of the synthesis gas resulting from the gasification of biomass,
- a condensing boiler (15) connected to the outlet of the burner (13) to, on the one hand, cool the combustion fumes coming from the burner (13) and comprising in particular carbon dioxide (CO ₂ ) and water vapor, and on the other hand, condense the water vapor contained in said combustion fumes,
- a condenser (16) connected to the outlet of the condensing boiler (15) for further cooling the combustion fumes from the condensing boiler (15), and separating the water vapor and carbon dioxide (CO ₂ ) from said fumes, and
- means for recovering carbon dioxide ( _CO2 ) separated from the water vapor in the condenser (16) and means for storing and/or distributing this recovered carbon dioxide ( _CO2 ) to one or more cultivation greenhouses,
the installation (1) further comprising at the outlet of the gasifier (12) means for generating heat and/or electricity (14) from the synthesis gas resulting from the gasification of biomass. Installation (1) according to claim 1, further comprising means for treatment by filtration (UF) of the synthesis gas resulting from the gasification of biomass in the gasifier (12) before its injection into the burner (13). Installation (1) according to claim 1 or 2, in which the heat and/or electricity generation means (14) comprise a generator set supplied with synthesis gas from the gasification of biomass. Installation (1) according to one of claims 1 to 3, further comprising means adapted to evacuate part of the ash of carbonaceous material resulting from the gasification in the gasifier (12). Installation (1) according to one of claims 1 to 4, in which the gasifier (12) is of the co-current fixed bed type. Installation (1) according to one of claims 1 to 5, comprising means for pre-treating the biomass by drying before introducing the biomass into the gasifier (12). Method for producing carbon dioxide and energy from biomass using the installation (1) according to one of claims 1 to 6, in which:
- biomass is introduced into the gasifier (12),
- the synthesis gas is evacuated from the gasifier (12) to introduce it partly into the burner (13) adapted for the combustion of synthesis gas and partly into the heat and/or electricity generation means (14),
- the fumes from combustion are treated in a condensation boiler (15) then in a condenser (16) to extract carbon dioxide ( _CO2 ) and distribute it to one or more greenhouses.
[Fig 1]