Method of controlling a wet scrubber useful for removing sulphur dioxide from a process gas
A wet scrubber for cleaning a process gas containing sulphur dioxide comprises an absorption vessel for contacting the process gas with an absorption liquid to absorb sulphur dioxide from the process gas, a sensor for measuring a concentration in the absorption liquid, and a control unit. The control unit is adapted to receive a measurement signal from the sensor and to control, based on the measured concentration, at least one wet scrubber operating parameter influencing the concentration in the absorption liquid.
1. A method of controlling a wet scrubber used to clean a process gas containing sulphur dioxide, the method comprising:
contacting the process gas with an absorption liquid in an absorption vessel to absorb sulphur dioxide from the process gas;
measuring a concentration of sulphite in the absorption liquid to obtain a sulphite concentration measurement; and
controlling, based on the sulphite concentration measurement as compared to a set point therefor, at least one scrubber operating parameter influencing the concentration of sulphite in the absorption liquid, by effecting, when the sulphite concentration measurement exceeds the set point, a reduction of a pH of the absorption liquid accompanied by at least one of:
increasing a liquid to gas ratio in the absorption vessel; and
increasing a supply of an absorption enhancing additive to the absorption liquid.
2. The method according to claim 1 , further comprising:
effecting, when the sulphite concentration measurement exceeds the set point, at least one of:
increasing a supply of a gas containing oxygen to the absorption liquid;
supplying an absorption enhancing additive to the absorption liquid.
3. The method according to claim 1 , further comprising:
effecting, when the sulphite concentration measurement is below the set point, at least one of:
reducing a supply of a gas containing oxygen to the absorption liquid;
increasing a pH of the absorption liquid; and
reducing a supply of an absorption enhancing additive to the absorption liquid.
4. The method according to claim 1 , further comprising:
effecting, when the sulphite concentration measurement is below the set point, an increase of a pH of the absorption liquid accompanied by at least one of:
reducing a liquid to gas ratio in the absorption vessel; and
reducing a supply of an absorption enhancing additive to the absorption liquid.
5. The method according to claim 1 , further comprising:
collecting absorption liquid after sulphur dioxide absorption by the absorption liquid from the process gas; and
measuring a sulphite concentration of the collected absorption liquid to obtain a sulphite concentration measurement prior to mixing the absorption liquid with absorbent material.
6. The method according to claim 1 , further comprising:
collecting absorption liquid after sulphur dioxide absorption by the absorption liquid from the process gas; and
measuring a sulphite concentration of the collected absorption liquid to obtain a sulphite concentration measurement prior to mixing the absorption liquid with absorbent material and prior to bubbling an oxygen containing gas through the absorption liquid.
7. The method according to claim 1 , further comprising:
collecting absorption liquid after sulphur dioxide absorption by the absorption liquid from the process gas; and
measuring the concentration of sulphite within 1 minute of collecting the absorption liquid from the absorption vessel.
8. The method according to claim 1 , further comprising:
collecting absorption liquid after sulphur dioxide absorption by the absorption liquid from the process gas and prior to bubbling an oxygen containing gas through the absorption liquid;
measuring a first concentration of sulphite of the collected absorption liquid to obtain a first measurement;
collecting absorption liquid after the absorption liquid is exposed to a bubbling of oxygen containing gas;
measuring a second concentration of sulphite of the exposed absorption liquid to obtain a second measurement, and
comparing the first measurement to the second measurement to determine whether the concentration of sulphite is increasing or decreasing.
9. The method according to claim 1 , further comprising:
detecting, based on a comparison between a first sulphite concentration measurement and a second sulphite concentration measurement, if the sulphite concentration of the absorption liquid is increasing; and
effecting, when the sulphite concentration is increasing, at least one of:
increasing a supply of a gas containing oxygen to the absorption liquid;
reducing a pH of the absorption liquid; and
supplying an absorption enhancing additive to the absorption liquid.