Method and system for gas scrubbing of aerosol-containing process gases

Abstract

The invention relates to a method and to a system for gas scrubbing of aerosol-containing process gases using an amine-containing solvent as scrubbing agent, which is brought into contact with the process gas in an absorber column (9) and which is regenerated in a desorber column (13) and after cooling is delivered to the absorber column (9) again. The water vapor concentration of the process gas which is not saturated with water vapor is increased with water before the gas scrubbing in the absorber column (9), preferably to a degree of saturation of >0.8, such that water is condensed out of the gas phase on aerosol particles contained in the process gas, and in a following method step the aerosol particles which have grown in size are precipitated out of the process gas before the gas scrubbing.

Claims

1. A method for gas scrubbing of process gas containing aerosol particles, comprising: using an amine-containing solvent as a scrubbing agent, bringing the scrubbing agent into contact with the process gas containing the aerosol particles in an absorber column and gas scrubbing the process gas containing the aerosol particles with the scrubbing agent in the absorber column, and regenerating the scrubbing agent in a desorber column and, after cooling, feeding the scrubbing agent back to the absorber column, wherein a water vapor concentration of the process gas containing the aerosol particles is increased with water before the gas scrubbing in the absorber column, such that the water condenses on the aerosol particles present in the process gas to grow the aerosol particles in size, and that, in a following method step, precipitating the aerosol particles that have grown in size from the process gas before the gas scrubbing, wherein the water vapor concentration of the process gas is adjusted to a degree of saturation of >0.8 by passing it through a foam scrubber, dispersant scrubber, or bubble-layer scrubber in each case as a gas-liquid contact apparatus having perforated plates, roller plates or tube internals in which the gas flows through a liquid layer or foam layer.

2. The method as claimed in claim 1, wherein the concentration of the aerosol particles having a diameter<0.2 m in the process gas is adjusted before the gas scrubbing to <60 000/m.sup.3 of process gas.

3. The method as claimed in claim 1, wherein the aerosol particles, after increase in size by water vapor condensation, are precipitated in a corona-aerosol separator or in a wet electrostatic precipitator.

4. The method as claimed in claim 1, wherein the method comprises the gas scrubbing of flue gases from a power plant as aerosol-containing process gas, wherein the method comprises a wet flue gas desulfurization and also a CO.sub.2-capture downstream of the flue gas desulfurization as gas scrubbing.

Description

(1) The invention will be described hereinafter with reference to an exemplary embodiment illustrated in the drawings:

(2) In the drawings:

(3) FIG. 1 shows a method flowchart which illustrates the flue gas desulfurization of the flue gas from a fossil-fuelled steam generator that is illustrated schematically and

(4) FIG. 2 shows a schematic method flowchart of the CO.sub.2 scrubber connected downstream of the flue gas desulfurization unit.

(5) First reference is made to FIG. 1.

(6) The flue gas desulfurization unit 1 shown there is arranged, for example, in the flue gas pathway of a coal-fired power plant (that is not shown). The dirty gas from the coal firing is very largely freed from fly ash in an electrostatic precipitator 2.

(7) An induced draft having a first fan 3 is connected downstream of the electrostatic precipitator 2, which first fan 3 compensates for the pressure drops in the flue gas pathway. That is to say flue gas that is not saturated with water is first fed to a scrubbing tower 4 (wet scrubbing) of the flue gas desulfurization unit 1. According to whether heat decoupling from the flue gas before entry into the flue gas desulfurization unit 1 is provided or not, the temperature of the flue gas is typically between 105 C. and 140 C.

(8) Within the scrubbing tower 4, the flue gas is conducted in counterflow to a limestone suspension (CaCO.sub.3/milk of lime). The CaCO.sub.3 is oxidized with the SO.sub.2 of the flue gas to form calcium sulfate and is discharged via the sump 5 of the scrubbing tower 4. In this case, the flue gas is cooled to a temperature from about 50 C. to 65 C. The lime suspension collecting in the sump 5 of the scrubbing tower 4 is discharged and, after the gypsum is separated off in hydrocyclones, is recirculated to the scrubbing tower 4. At the top of the scrubbing tower 4, droplet separators 6 are provided which are flushed with process water. Depending on the power plant type, and/or interconnection variants, the flue gas/process gas is heated downstream of the scrubbing tower 4.

(9) For example, the heat content can be displaced from the flue gas before entry into the scrubbing tower 4 to the flue gas after exit from the scrubbing tower 4 or to the boiler feed water preheating or combustion air preheating. Such a heat displacement is not necessarily necessary, and therefore is not shown for reasons of simplicity.

(10) A further scrubbing column 7 is connected as fine scrubber downstream of the scrubbing tower 4. In the fine scrubber, by means of structured or unstructured packings, using cooled circulation water, for example using flue gas condensate, an aqueous NaOH solution is brought into contact in counterflow with the flue gas, in order to achieve further cooling of the flue gas and remove any remainder of SO.sub.2. The condensate is collected in the sump 8 of the fine scrubber and utilized as circulation water.

(11) Before the flue gas is introduced into the absorber column 9 of a CO.sub.2 scrubber 10 shown in FIG. 2, there is a slight pressure elevation by means of a second fan 11.

(12) The CO.sub.2 present in the process gas and/or flue gas is scrubbed out in the absorber column 9 at a low temperature (for example 40 C. to 60 C.) using an aqueous solvent, for example a mixture of water with monoethanolamine (MEA). After the CO.sub.2-loaded solvent/scrubbing agent has been preheated via a cross-flow heat exchanger 12, the CO.sub.2-loaded solvent that is thus preheated is introduced into a desorber column 13, which is also termed a stripper. Here, superheated steam at about 110 C. to 130 C. flows against the liquid solvent from bottom close to the desorber sump, which superheated steam is generated in a reboiler 14 by heating a substream of the solvent, for example using low-pressure steam. Here, steam, for example having a vapor pressure of 4 bar, can be used, which was tapped off between the medium-pressure and low-pressure part of a steam turbine of the power plant. At the top of the absorber column 9, the purified process gas is discharged as clean gas.

(13) In order to suppress as far as possible a fine fog discharge containing solvent and/or scrubbing agent at the top of the absorber column 9, and thereby suppress as far as possible a scrubbing agent emission or amine emission, it is provided according to the invention to quench flue gas/process gas at the sites A, B or C with water. Positions A, B or C can designate, for example, water injection coolers or steam feeds. The positions A, B are arranged downstream of the induced draft of the flue gas stream upstream of the scrubbing tower 4 and also upstream (A) or downstream (B) of an optional heat displacement system, position C is situated within the scrubbing tower 4 and denotes, for example, a unit in which quenching, aerosol particle precipitation and desulfurization proceed within the unit.

(14) A precipitation of the very fine aerosol particles that have grown in size by the quenching proceeds in each case in droplet separators 6, 7 or wet electrostatic precipitators 15 that are connected downstream of the scrubbing tower 4 and the fine scrubber 7. The invention is to be understood such that, optionally, a single wet electrostatic precipitator 15 is sufficient in order to retain from the flue gas the aerosol particles that have increased in size by the quenching. These aerosol particles, according to findings of the applicant, are primarily responsible for the amine fog discharge from the absorber column 9.

LIST OF REFERENCE SIGNS

(15) 1 Flue gas desulfurization unit 2 Electrostatic precipitator 3 First fan 4 Scrubbing tower 5 Sump of the scrubbing tower 6 Droplet separator 7 Fine scrubber 8 Sump of the fine scrubber 9 Absorber column 10 CO.sub.2 scrubber 11 Second fan 12 Cross-flow heat exchanger 13 Desorber column 14 Reboiler 15 Wet electrostatic precipitator