A process for separating a mixture containing CO2, water, and at least one of the following components: SOx, NOx

Abstract

Title: Process for separating a mixture containing CO2, water, and at least one of the following components: SOx, NOx. The process comprises washing the mixture in a scrubbing tower and / or compressing it to produce condensate. The washed mixture is then separated by a CO2 capture process comprising a partial condensation and / or liquefaction and / or solidification step. The condensate is vaporized and discharged to the atmosphere through at least one pipe. After vaporization, the vaporized condensate is superheated to a temperature sufficient to prevent condensation in the pipe by means of residual heat available within the CO2 capture process. No figure

Description

Title of the invention: Method for separating a mixture containing CO2, water and at least one of the following components; SOx, NOx

[0001] The present invention relates to a process for separating a mixture containing CO2, water and at least one of the following components: SOx, NOx.

[0002] The various stages of CO2 capture via a unit using a partial condensation and / or distillation and / or solidification stage generate the formation of condensates upstream of the low-temperature separation (washing, compression stages, drying). The condensates are collected and then treated in treatment units; The condensates can contain a wide spectrum of impurities such as HNO3, H2SO4, HCl, NaOH, NH3, dust (heavy metals)... and generally have a low pH (<2 unless the pH is regulated by the injection of a basic agent). They are therefore treated in treatment units whose objective is to achieve a water quality at the outlet of the station that complies with the legislative framework for the discharge of liquid effluents into the environment.Biological treatment is possible, but if heavy metals are present, biological treatment is generally not possible and a physicochemical treatment will more generally be chosen, consisting of subsequent steps of coagulation, flocculation, retention and neutralization. The contaminants will be separated from the water and will be eliminated in the form of residual sludge (dewatered by means of a chamber filter press or a centrifuge).

[0003] These treatment units are expensive in terms of operating costs and investment.

[0004] In the following, the customer is the legal person who produces by an industrial process a gas to be treated by CO2 capture. This industrial process of the customer can produce gases to be released into the atmosphere.

[0005] According to an object of the invention, there is provided a method for separating a mixture containing CO2, water and at least one of the following components; SOx, NOx in which the mixture is washed in a washing tower and / or compressed producing condensate, the washed mixture is separated by a CO2 capture method comprising a step of partial condensation and / or liquefaction and / or solidification, the condensates are vaporized and sent to the atmosphere through at least one pipe, the vaporized condensates being superheated after vaporization to a temperature sufficient to avoid any condensation in the at least one pipe by means of 1. residual heat available within the CO2 capture process and / or a process that produces the mixture) and / or 2. with an external heat supply.

[0006] Innovations:

[0007] Condensates cannot be returned to the atmosphere via a stack without preliminary vaporization and superheating because of the risk of acid rain (H2SO4) formation. The largest portion of condensates from a CO2 capture process is generated by the water or basic liquid scrubbing step.

[0008] The materials of the heating means on the vaporization side must be carefully selected to take into account the risk of formation of droplets highly concentrated in SO4 2

[0009] The innovations proposed below are a priori especially valid for small CO2 capture units for which the treatment of condensates would be too costly, either by the investment of a dedicated treatment unit, or by treatment by an external company.

[0010] Note that the acid condensates are already basic in the fumes and therefore released into the atmosphere, the invention proposing to continue to release them into the air while capturing the CO2, which avoids operating and investment costs and the use of agents for the treatment of the condensates.

[0011] The proposed innovation is particularly advantageous when the treatment of condensates is complicated (for example depending on the presence of certain impurities such as heavy metals) and the site does not need to recover the water contained in the fumes (i.e. water produced by combustion).

[0012] 1 / The condensates generated (or part of them) by the different stages separation of a CO2 capture process are vaporized and superheated to a sufficient temperature (depending on SO3 content) to avoid any condensation in the pipes using residual heat available within the process (CO2 capture process and / or a customer process that produces the mixture) and / or with an external heat input and then sent to the atmosphere (via dedicated vent) (or even recycled to the customer process) at a sufficiently high height. This solution creates a point of emission of effluents to the atmosphere, probably additional (at the vent of the residual N2). The technology and material of the vaporizer must be selected with care: at high temperature, the risk of corrosion by H2SO4 and HCl is high.

[0013] 2 / The vaporized condensates can be mixed with the residual N2 and sent to the event (operator, customer).

[0014] The condensates or a mixture of condensates and waste nitrogen must be vaporized and superheated beforehand. The heating temperature depends on the amount of SO2 / H2SO4 that the condensates contain.

[0015] The mixing temperature of the two gases must be sufficiently high (>250°C) to avoid the formation of acid rain.

[0016] Solutions 1 / and 2 / are potentially subject to permit applications or environmental constraints (generation of an additional source of effluent to the atmosphere).

[0017] 3 / Solution 3) The condensates of the process can be vaporized separately (by the fumes and / or external heat) then injected into the customer's chimney fumes.

[0018] The heat of the fumes can be used to vaporize the condensates (for example in a coiled exchanger).

[0019] 4 / Solution 4) The customer's fumes may be overheated and the condensates liquids sprayed by direct contact with fumes.

[0020] The spray enclosure must be appropriately sized to prevent the acid droplets from having time to touch the walls.

[0021] The choice of materials is a problem that should not be neglected to avoid the risk of corrosion.

[0022] Solutions 3 / and 4 / are the most promising, especially when the CO2 capture unit only treats part of the fumes. Generally, the fumes are heated to a temperature equal to the dew point temperature of the acid plus a margin of 25°C to avoid the risk of corrosion by H2SO4 in the flue duct and the chimney (or vent).

[0023] The dew point temperature of H2SO4 can be estimated according to the following formula:

[0024] (by David A. Lewandowski (2000). Design of Thermal Oxidation Systems for Volatile Organic Compounds, Ist Edition. CRC Press. ISBN 1-56670-410-3, https: / / citizendium.org / wiki / Acid_dew_point)

[0025] [Chem.l] 1000 —— = 1.7842 - 0.0269 " 0.1029 logw(PSO3) 4- 0.0329 / 0510(^20)^510(^03) T

[0026] With T the dew point temperature of the acid in Kelvin and P the partial pressure in atm.

[0027] a) acid dew point of H2SO4 in acid condensates

[0028] With 80 ppm of H2SO4 in condensates at 2 bara (99.7% mol of water),

[0029] T = 276.5°C

[0030] b) acid dew point of H2SO4 in a nitrogen-rich gas

[0031]

[0032]

[0033]

[0034]

[0035] With 80ppm of H2SO4 in a vent gas at 1.013 bara (20.9%mol of water), T = 213.2°C c) dew point of H2SO4 acid in a flue gas With 80ppm of H2SO4 in a flue gas at 0.96 bara (17%mol of water), T = 206.7°C

Claims

[Claim 1] Claims A method for separating a mixture containing CO2, water and at least one of the following components; SOx, NOx wherein the mixture is washed in a washing tower producing condensates, the washed mixture is separated by a CO2 capture process comprising a step of partial condensation and optionally liquefaction or solidification to produce CO2, the condensates are vaporized and sent to the atmosphere through at least one pipe, the vaporized condensates being superheated after vaporization to a temperature sufficient to avoid any condensation in the at least one pipe by means of residual heat available within the CO2 capture process.