Method and apparatus for washing a gas stream

Abstract

Title of the invention: Method and apparatus for washing a gas stream. In a gas stream washing process, liquid (7) from the scrubbing tower (K) is vaporized (E1) to cool ambient air (19), which is then used to cool water (25), producing cooling water (27) for use upstream or downstream of the washing process. Abstract figure: Figure 1

Description

Title of the invention: Method and apparatus for washing a gas stream

[0001] The present invention relates to a method and apparatus for washing a gas stream. The gas stream can be a high-temperature gas (typically at least 150°C, or even at least 180°C), for example, generated by combustion. It can also be at ambient temperature. It contains at least 15% mol of carbon dioxide on a dry basis and is treated to recover the CO2 and prevent its release into the atmosphere.

[0002] Climate change is one of the greatest environmental challenges. The increase in atmospheric carbon dioxide concentration is largely responsible for global warming. Human-caused CO2 is primarily emitted into the atmosphere by the combustion of fossil fuels in thermal power plants. Thermal power plants, through the combustion of fuels, release heat that can be used to produce steam and potentially mechanical or electrical energy. Combustion fumes release significant quantities of CO2 into the atmosphere. The combustion process leads in particular to the production of fumes consisting mainly of CO2, water (for example, 30 mol% water), gases from the air also called non-condensable gases (N2, Ar, O2), and acidic gases called NOx and SOx, as well as significant quantities of dust.

[0003] During the treatment and purification stages, in particular compression (followed by refrigeration), SOx and / or NOx, generic names which include all sulfur oxides and all nitrogen oxides, will generate acidic condensates, including: nitric, nitrous, sulfuric, sulfurous acid... which must be avoided to limit the risk of corrosion.

[0004] The purpose of washing is to lower the temperature of the combustion gas, to remove suspended matter, for example dust, and acidic components contained in the combustion gas.

[0005] Depending on the composition of the combustion gas, the washing can be carried out with water or water made basic by the addition of a base.

[0006] Basic wet scrubbing is a recognized technology in flue gas treatment for removing acidic gases contained in flue gases. Sodium bases are preferred because they offer a good compromise between their performance (solubility and therefore ability to prevent precipitation) and their availability and associated cost. Examples include: NaOH, Na2CO3, NaHCO3....

[0007] The gas stream comprising at least one NOx and / or at least one SOx and at least 15 mol% dry CO2 enters countercurrently into a tower serving as A gas / liquid contactor is used for basic wet scrubbing before the gas exits the top of the tower. The gas is enriched with CO2 and has a reduced concentration of at least one NOx and / or at least one SOx. Caustic soda and / or water are introduced at the top of the contactor to scrub the gas stream. At the bottom of the gas / liquid contactor, the liquid that has been in contact with the stream is drawn off. This liquid, containing acidified water, may also contain solid impurities (particles such as dust from the combustion gas) and / or dissolved minerals.

[0008] The gas stream exiting the tower has a reduced NOx and / or SOx content and is then compressed in a compressor and dried in a dryer before being sent to a CO2 separation unit to remove the nitrogen and oxygen it contains. This unit operates by partial condensation and / or distillation, producing a CO2-rich fluid. This CO2-rich fluid is sometimes pressurized before being used by a customer or sequestered. The unit also produces at least one gas enriched in nitrogen and / or oxygen.

[0009] A closed-circuit cooling water network is generally used to cool the gas coming from the contactor at the outlet of the compressor compression stages and upstream of the dryer.

[0010] The liquid exiting the washing tower tank is generally treated to neutralize the harmful substances it contains and is sent to a water treatment unit.

[0011] The present invention consists of using the liquid exiting the scrubber tower tank to cool water. The liquid is optionally treated to reduce the amount of suspended solids and dissolved minerals and is then evaporated in an air stream at the inlet of the air coolers of a cooling water circuit in order to lower the air temperature and consequently lower the temperature of the chilled water produced by the air coolers. This chilled water is then used to cool a compressor in the CO2 separation process, resulting in a reduction of the energy required to compress the combustion gases from which the CO2 is to be captured.

[0012] According to one object of the invention, a method for washing a gas stream is provided in which: i. a gas stream comprising at least one NOx and / or at least one SOx and / or suspended matter and at least 15 mol% CO2 on a dry basis is sent to a scrubbing tower in which it is cooled and scrubbed with water and / or an alkaline liquid to produce a CO2-enriched gas at the top of the tower and a tank liquid enriched with at least one NOx and / or at least one SOx and / or suspended matter in the tower tank, ii. at least a portion of the tank liquid is optionally filtered and / or demineralized to produce a purified liquid iii. at least a portion of the tank fluid from step i) or the purified fluid from step ii), if present, is used to cool an airflow by direct contact evaporation or indirect heat exchange, forming a cooled airflow and iv. The cooled air flow is used to cool a water flow by indirect or direct heat exchange, forming a cooled water flow.

[0013] According to other optional aspects of the invention, it is provided that: • Liquid from the scrubber tower is vaporized to cool ambient air which is then used to cool water, producing cooling water for use upstream or downstream of the scrubber tower. • at least part of the tank liquid from step i) or the purified liquid from step ii) if present is pressurized by a pump upstream of step iii). • The flow of cooled water is used to cool a compressed gas between two stages of a compressor and / or after the last stage of a compressor by heat exchange, the compressor being a compressor i. Of the gas flow upstream of the tower or ii. CO2-enriched gas extracted from the top of the tower or iii. Of a CO2-enriched product produced by partial condensation and / or distillation of the CO2-enriched gas drawn from the top of the tower, this gas containing oxygen and / or nitrogen and / or carbon monoxide. • at least part of the tank liquid is treated upstream of its vaporization to remove at least partially at least one NOX and / or at least one SOX and / or the suspended matter it contains, the removed components being disposed of. • at least part of the tank liquid from step i) or the purified liquid from step ii) if present is stored in upstream storage of vaporization. • at least a portion of the tank liquid from step i) or the purified liquid from step ii), if present, is not used to cool the airflow by evaporation if the ambient temperature is below a threshold and is stored in storage if the ambient temperature is below the threshold. • at least a portion of the tank liquid from step i) or the purified liquid from step ii), if present, is used to cool an airflow by evaporation only if the ambient temperature is higher than the threshold. • the liquid flow is vaporized by nebulization or in adiabatic air coolers or in hybrid air coolers.

[0014] According to one object of the invention, a gas stream washing apparatus is provided, comprising a washing tower, optionally a treatment unit, optionally a storage unit, an evaporator, a heat exchange means, and means for sending a gas stream comprising at least one NOx and / or at least one SOx and / or suspended matter and at least 15 mol% CO2 on a dry basis to the scrubbing tower for cooling and scrubbing with water and / or an alkaline liquid to produce a CO2-enriched gas at the top of the tower and a tank liquid enriched with at least one NOx and / or at least one SOx and / or suspended matter in the tower tank, means for removing the tank liquid from the tower, means for sending at least a portion of the tank liquid to the evaporator for vaporization by direct or indirect heat exchange with an air flow, optionally after treating at least a portion of the tank liquid in the treatment unit to purify it and / or after storing at least a portion of the tank liquid in the storage,means for sending the cooled air flow into the evaporator by means of heat exchange, for indirect or direct heat exchange with a water flow to be cooled, forming a cooled water flow.

[0015] A gas stream separation apparatus may include a scrubber as described above, a compressor, and a partial distillation and / or condensation separation apparatus connected to the scrubber for separating the CO2-enriched gas, forming a CO2-enriched product fluid, from the gas, and means for sending the cooled water flow to cool the compressor, the compressor being a compressor i. From the gas stream upstream of the tower or ii. CO2-enriched gas extracted from the top of the tower or iii. Of a CO2-enriched product produced by partial condensation and / or distillation of the CO2-enriched gas drawn from the top of the tower.

[0016] Evaporation of the liquid from the tower can be achieved in different ways: nebulization (in English “fogging”), in adiabatic air coolers, in hybrid air coolers of the WSAC type (in English “Wet Surface Air Coolers”).

[0017] Depending on the impurities contained in the condensate and depending on the quality of the water required for the equipment carrying out the evaporation, the treatment unit may include a filtration to reduce / remove suspended matter and a demineralization chain to reduce / remove dissolved species.

[0018] In all cases, the treatment unit will allow the degassing of harmful gases dissolved in the condensate by sending them to the air through a chimney or to another secure location and thus avoiding the risk of poisoning for any operator handling these effluents.

[0019] The liquid flow rate produced in the tower is typically insufficient to ensure significant continuous evaporative cooling, 24 hours a day. Therefore, in order to obtain a higher condensate flow rate, the liquid from the tower is stored, after any necessary treatment, in a tank. Only when the ambient temperature falls below a certain threshold is the liquid removed from storage and then pumped to the system. evaporation. In this way, the liquid produced during the night (and more generally during the cooler hours of the day) can be used during the day when the ambient temperature is highest and the need for cooling is greatest.

[0020] The invention will be described in more detail with reference to the figure.

[0021] [Fig-1] illustrates a method according to the invention.

[0022] [Fig-1] shows a washing process in which a gas 1 produced by combustion preferably contains at least 15 mol% of carbon dioxide, water, nitrogen and / or oxygen and / or argon and SOx and / or NOx and / or suspended matter, such as dust.

[0023] In this gas stream washing process, liquid 7 from the washing tower K is vaporized El to cool ambient air 19 which is then used to cool water 25 producing cooling water 27 for use upstream or downstream of the washing process.

[0024] The hot combustion gas 1 is sent to a scrubbing tower K, which is fed at its top by a flow of water 3 recovered from a tank in the same tower and supplemented, if necessary, with caustic soda 2. The cooled gas 5, scrubbed of SOx and / or NOx and / or suspended matter (dust), exits at the top of the tower. The scrubbing can be carried out at atmospheric pressure or, if necessary, at a higher pressure, for example, at least 2 bar abs.

[0025] In the tower tank, the part 7 of liquid which is not recycled at the top of the washing tower K is enriched in SOx and / or NOx and / or suspended matter and can be sent to a treatment unit T where it is for example filtered to remove the solid particles it contains and / or demineralized to a higher or lower level depending on the level of demineralization required by the heat exchanger El where evaporation takes place which cools the ambient air drawn in by the air coolers of the cooling water circuit.

[0026] The treated liquid 8 is preferably sent to a storage S, which can be a natural basin.

[0027] The liquid 11 at the outlet of the treatment unit T concentrates the SOx and / or NOx and / or suspended matter removed from the treated liquid 8 and can be disposed of in accordance with the regulations in force.

[0028] If necessary, through outlet 9 the treatment unit T can also remove any gases that may be dissolved and that it would not be desirable to have in the treated liquid 8.

[0029] From storage S, the treated liquid 8 is pressurized as liquid 13 in a pump P, forming a pressurized liquid 15. The liquid 15 is sent to a heat exchanger El (or evaporator) where it evaporates by indirect or direct heat exchange with a flow of air 19 that is cooled within it. Evaporation can take place by nebulization by projecting the liquid 15 in fine droplets into the air. Alternatively, the exchanger El may include adiabatic air coolers operating by spraying or trickling the liquid into the air or in hybrid air coolers.

[0030] The water vapor 17 formed by the evaporation of water 15, for example by direct contact with air 19, exits the heat exchanger El, and the air cooled 21 in the exchanger El is sent to a heat exchanger E2 where it cools a flow of water 25 by direct or indirect heat exchange. The cooled water 27 is sent to a heat exchanger E3 where it cools the compressed gas in the compressor C, this gas being the overhead gas of the tower K. Thus, the exchanger E3 serves as the final cooler for the compressor C. The water can also cool this compressor C at an interstage.

[0031] The heated air 23 exits the exchanger E3.

[0032] The gas compressed in compressor C is dried, cooled and separated by distillation and / or partial condensation in separation unit CC to produce a CO2-rich flow 29. This allows the removal of oxygen and / or nitrogen and / or argon and / or carbon monoxide it contains.

[0033] The CO2-rich flow 29 can be compressed in a compressor, which can be cooled after the final stage or in interstage by water 27.

[0034] Otherwise, the water 27 can cool a final stage or an interstage of the compressor of the gas flow 1 if the tower K operates under pressure.

[0035] Otherwise the cooling water 27 can be used anywhere upstream or downstream of the washing tower K.

[0036] To take advantage of cooler ambient temperatures, the process can operate by storing cold liquid in the storage tank S. When the ambient temperature and / or the air temperature 19 is below a threshold, for example 15°C at night or in winter, it is not necessary to send liquid (or such a large flow rate of liquid) to the evaporator, since the air is already cold enough to cool the water in the heat exchanger E2 to the required temperature. Otherwise, in this case, it may be sufficient to send a reduced flow rate of liquid, since the air is almost cold enough to cool the water to the required temperature in the heat exchanger E2.

[0037] Below this ambient temperature threshold, which can be measured by determining the outside temperature or that of the air 19, liquid is stored in a storage container, preferably thermally insulated. When the ambient temperature and / or the air temperature 19 rises above the threshold, for example 15°C, 30°C, it may be necessary to cool the air (or to cool the air further) and therefore the liquid from the storage container is drawn off to evaporate in the heat exchanger El (or a greater flow rate of liquid is drawn off to evaporate in the heat exchanger El than during the period when the temperature is below the threshold).

[0038] The flow rate of vaporized liquid 17 from storage S can be zero if the temperature The ambient temperature is sufficiently low. In this case, liquid from storage S is sent to the heat exchanger El only if the ambient temperature is above a temperature threshold. Thus, the pump P only operates if the ambient temperature is above a temperature threshold, for example, 15°C or 30°C.

Claims

1.

2.

3.

4. Claims Process for washing a gas stream in which: i. a gas stream (1) comprising at least one NOx and / or at least one SOx and / or suspended matter and at least 15 mol% CO2 on a dry basis is sent to a scrubbing tower (K) in which it is cooled and scrubbed using water (4) and / or an alkaline liquid (2) to produce a CO2-enriched gas (5) at the top of the tower and a bottom liquid (3, 7) enriched in the at least one NOx and / or the at least one SOx and / or suspended matter in the bottom of the tower, ii. at least a portion (7) of the tank liquid is optionally filtered and / or demineralized to produce a purified liquid (8, 13) iii. at least a portion of the tank liquid (7) from step i) or the purified liquid (8) from step ii), if present, is used to cool an air flow (19) by evaporation in direct contact or by indirect heat exchange forming a cooled air flow (21) and iv. the cooled air flow is used to cool a water flow (25) by indirect or direct heat exchange forming a cooled water flow (27). Method according to claim 1 in which at least part of the tank liquid (7) from step i) or the purified liquid (13) from step ii) if present is pressurized by a pump (P) upstream of step iii). Method according to claim 1 or 2 in which the cooled water flow (27) serves to cool a compressed gas between two stages of a compressor and / or after the last stage of a compressor (C) by heat exchange, the compressor being a compressor i. From the gas flow (1) upstream of the tower (K) or ii. CO2-enriched gas (5) drawn off at the top of the tower or iii. A CO2-enriched product (29) produced by partial condensation and / or distillation of the CO2-enriched gas withdrawn at the top of the tower, this gas containing oxygen and / or nitrogen and / or carbon monoxide. Method according to one of the preceding claims in which the at least a portion of the tank liquid (7) is treated upstream of its vaporization to at least partially eliminate the at least one NOX and / or the at least one SOX and / or the suspended matter that it contains, the eliminated components being arranged (9, 11).

5. Method according to one of the preceding claims in which at least one part (7) of the tank liquid from step i) or the purified liquid (8) from step ii) if present is stored in a storage (S) upstream of the vaporization.

6. A method according to claim 5 wherein the at least part of the tank liquid (7) of step i) or the purified liquid (8) of step ii), if present, is not used to cool the air flow (19) by evaporation if the ambient temperature is below a threshold and is stored in the storage (S) if the ambient temperature is below the threshold.

7. A method according to claim 6 wherein the at least part of the tank liquid (7) from step i) or the purified liquid (8) from step ii), if present, is used to cool the air flow (19) by evaporation only if the ambient temperature is higher than the threshold.

8. Method according to one of the preceding claims in which the liquid flow (15) is vaporized by nebulization or in adiabatic air coolers or in hybrid air coolers (El).

9. Apparatus for washing a gas stream comprising a washing tower (K), optionally a treatment unit (T), optionally a storage (S), an evaporator (El), a heat exchange means (E2), means for sending a gas stream (1) comprising at least one NOx and / or at least one SOx and / or suspended matter and at least 15 mol% of CO2 on a dry basis to the washing tower to cool it and wash it using water (3) and / or an alkaline liquid (2) to produce a CO2-enriched gas (5) at the top of the tower and a bottom liquid (3, 7) enriched in the at least one NOx and / or the at least one SOx and / or suspended matter in the bottom of the tower, means for removing the bottom liquid from the tower, means for sending at least a portion (7) of the bottom liquid to the evaporator to vaporize by direct or indirect heat exchange with an air flow,optionally after having treated at least part of the tank liquid in the treatment unit to purify it and / or after having stored at least part of the tank liquid in the storage, means for sending the cooled air flow (21) into the evaporator by means of heat exchange for indirect or direct heat exchange with a water flow (25) to, cool forming a cooled water flow (27).

10. Apparatus for separating a gas stream (1) comprising a washing apparatus according to claim 9, a compressor (C) and a distillation and / or partial condensation separation apparatus (CC) connected to the washing apparatus for separating the CO2-enriched gas forming a CO2-enriched product fluid relative to the gas, means for sending the cooled water flow to cool the compressor, the compressor being a compressor i. From the gas flow (1) upstream of the tower or ii. CO2-enriched gas (5) drawn off at the top of the tower or iii. Of a CO2-enriched product (29) produced by condensation partial and / or distillation of the CO2-enriched gas drawn off at the top of the tower.

Images