Air pollution control engineering   Part 2. Air pollution control engineering Gaseous Particulates

Control of Sulfur Oxides (SOx) Emission of SOx one of the major causes of acid precipitation SOx emission control areas

London fog event of December 1952

yearly moving-average month average Sulfur dioxide in Brussels-Capital Region

Evolution of SO2 emissions in Belgium since 1990 Target fixed by the Federal Government Trend differs according to the industry / activity sector

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Abatement of SO2 Selection of fuel type Pre-treatment of the fuel (before use) Flue gas desulfurization (FGD) s

Sulphur compounds found in fossil fuels Hydrogen sulphide H2S s Ethyl-mercaptan Ethane C2H5-SH C2H6   Boiling point 35°C -88.6°C this implies that sulfur compounds have a tendency to accumulate in heavy fractions when fuel is refined

Several options for control: Change to Low-sulfur fuel From 01 January 2015, maritime ships berthing within the EU are required to use fuel with a maximum sulphur content of 0.1%. Heavy fuels used in maritime transport are now targetted (especially in SOx emission control areas) MARPOL Annex VI

Coal-fired power plants - Desulphurization of a solid Sulfur in coal is either organic (usually about 60%) or inorganic (about 40%). The inorganic form is iron pyrite (FeS2) which has a higher density than coal. From grinded coal it is removed by elutriation or flotation. The removal of organic sulfur requires a chemical reaction that is accomplished best if the coal is gasified first. Gasified coal is like natural gas. Separation according to decreasing fall velocity s Principle of an elutriator

Coal-fired power plants – Desulphurization of a solid Sulfur in coal is either organic (usually about 60%) or inorganic (about 40%). The inorganic form is iron pyrite (FeS2) which has a higher density than coal. From grinded coal it is removed by elutriation or flotation. The removal of organic sulfur requires a chemical reaction that is accomplished best if the coal is gasified first. Gasified coal is like natural gas. Desulphurization through catalytic hydrogenation – Step 1 s ~ 400°C, ~ 50 bars

Desulphurization through catalytic hydrogenation – Step 2 Then a Claus converter is used to recover S vapor by staged combustion oven ~ 1000°C 300°C, catalytic reduction of SO2 Cobalt or Nickel as catalysers

Abatement of SO2 Selection of fuel type Pre-treatment of the fuel (before use) Flue gas desulfurization (FGD) s

Packed Bed Scrubber s

CA = concentration of A, [mol/L] Henry's Law states that the amount of a gas that dissolves into a liquid is proportional to the partial pressure that gas exerts on the surface of the liquid. where, CA = concentration of A, [mol/L] KH = equilibrium constant (Henry's Law constant), [mol/L-atm] pA = partial pressure of A, [atm] Flue gas desulfurization

Lime treatment reused in construction Lime scrubbing= The equipment and the processes are similar to those in limestone scrubbing. Lime Scrubbing offers better utilization of the reagent. The operation is more flexible. The major disadvantage is the high cost of lime compared to limestone.

A well-developed soda scrubber is the Wellman-Lord SO2 recovery process, which has found use in powerplants, refineries, sulfuric acid plants, and other industrial installations. The process utilizes a water solution of sodium sulfite (Na2SO3) for scrubbing and generates a concentrated SO2 (about 90%), in effect removing the SO2 gas from other flue gases. The flue gas from fossil powerplants (or nonferrous smelters) is first pretreated by cooling and removal of particulate matter, such as by electrostatic precipitators, prior to being sent to the absorber. In the absorber the water solution of sodium sulfite absorbs the SO2 in the pretreated flue gas to produce sodium bisulfite NaHSO3 according to SO2 + Na2SO3 + H2O -- 2NaHSO3 Actually the sodium bisulfite is sent to a forced-circulation evaporator-crystallizer (see sketch) via a surge tank. The evaporator-crystallizer is the herth of the system. The surge tank allows steady flow rates into it despite gas flow and concentration fluctuations. Through the application of low-pressure steam (such as from a turbine exhaust), the sulfite is regenerated. The desulfurized gas is reheated before going to the stack in order to improve atmospheric dispersion.

Wellman-Lord (regenerative) process Na2SO3 s regeneration