Flue gas desulfurization is the main measure used to control emission of sulfur dioxide in current coal-fired power plant. Among that, limestone-gypsum flue gas desulfurization is the most mature technology having been the mostly applied around the world. Valves are control device used to deal with fluid in pipeline system.
Main valves used in FGD system include globe valve, control valve, check valve and safety valve. Globe valve and control valve are mostly used for slurry. Globe valve is used to control transit and disconnection of media in pipeline, isolating pipeline system. Control valve is used to control flow rate and pressure of media in pipeline, maintaining technological parameters at expected range. Slurry pipeline which has been seriously worn should avoid throttling as far as possible. The system can use converter pump, switching valve or other operation methods. Control valve must not be used in case of being worn.
Features of media and valve choosing require that a large number of categories of valves are used in FGD system. Desulfurization project mostly contacts with media having wicked conditions. So, scaling, blocking, corrosion and abrasion are commonly seen in FGD system, which have strong impact on running rate of equipment in system. Therefore, before choosing valves correctly, we should know about features of media which valves contact with.
For FGD system, based on different contents of media, slurry is classified into limestone slurry, limestone gypsum slurry and gypsum slurry. The followings are their main features.
1. Slurry has granularity and abrasiveness. Mass fraction of limestone slurry can be as high as 55% and the density is 1500kg/m3.
2. PH ranges from 4 to 7. Slurry is inorganic substance shown as weak acid corrosivity.
3. Organic solution containing inert substances has corrosivity.
4. High flow velocity. In general design, flow velocity of slurry is controlled below than 2.5m/s while the maximum flow velocity can reach as high as 3.5m/s in practical operation, having particulated jet. Maximum velocity of circulating water and process water can reach as high as 5m/s.
5. High concentration. Desulfurization project is generally designed based on concentration of 20,000mg/l. However, the maximum concentration inside tower can be as high as 180,000mg/l. Concentration of waste water is about 40,000mg/l. Besides acid corrosion, slurry also has strong oxidability and reducibility.
For FGD system operation, take reliability and economy into consideration. Butterfly valve and control valve are mainly used in slurry pipeline of flue gas desulfurization.
