Flue Gas Desulfurization Project of Two 35t/h Circulating Fluidized Bed Boilers
2023-08-14 08:54:22The out-of-furnace desulfurization system of two 35t/h circulating fluidized bed boilers of ZBG group, including the technical requirements of the out-of-furnace desulfurization system, desulfurization main body and auxiliary equipment in terms of function design, structure, performance, control, equipment installation, commissioning, etc. Apart from civil foundation design and civil foundation construction, it is a turnkey project. The following introduces ZBG group ZG-35/3.82-M technical parameters and flue gas desulfurization project.
1. 35t/h boiler equipment and parameters
| Rated evaporation | t/h | 35 |
| Drum working pressure | MPa | 4.22 |
| superheater outlet pressure | MPa | 3.82 |
| superheated steam temperature | ℃ | 450 |
| Feed water temperature | ℃ | 100 |
| cold air temperature | ℃ | 20 |
| exhaust temperature | ℃ | 166.8 |
| Boiler Thermal Efficiency | % | 83.9 |
| Boiler unit flue gas resistance | Pa | 950 |
| Air Preheater Air Resistance | Pa | 6800 |
2. Flue gas desulfurization
At present, my country's coal-fired boiler flue gas desulfurization technology can be divided into four categories; (1) pre-combustion control - raw coal purification. (2) Control during combustion - fluidized bed combustion (CFB) and spray absorbent in the furnace. (3) Post-combustion control - flue gas desulfurization. (4) New technology (such as coal gasification/combined cycle system, liquid slag discharge burner). Among them, post-combustion flue gas desulfurization technology is mainly used. For flue gas desulfurization, the wet desulfurization process is the mainstream. Let's take a look at the comparison of several common boiler desulfurization processes:
| Desulfurization process name | Process principle | Process advantages | Process disadvantages |
| limestone plaster wet process | Use limestone powder slurry to wash flue gas, make limestone react with SO2 in flue gas to generate calcium sulfite, remove SO2 in flue gas, and then oxidize calcium sulfite to generate gypsum | High desulfurization rate: ≥95%, mature technology, suitable for all coal types, stable operation, good operating flexibility, easy to obtain desulfurizer, low operating cost, comprehensive utilization of by-product gypsum, and no secondary pollution | The process is longer and the investment is higher |
| Rotary Spray Drying | Make quicklime into lime slurry, spray the lime slurry into the flue gas, and make calcium hydroxide react with SO2 in the flue gas to form calcium sulfite | The technological process is simpler than the limestone gypsum method, and the investment is smaller | Low desulfurization rate: about 70-80%, small operating flexibility, high calcium-sulfur ratio, high operating costs, unusable by-products and prone to secondary pollution (decomposition of calcium sulfite) |
| Calcium spray tail humidification method in the furnace | Limestone powder is directly sprayed into the furnace of the boiler, and the limestone powder is decomposed into calcium oxide at high temperature, and the calcium oxide reacts with SO2 in the flue gas to form calcium sulfite. In order to improve the desulfurization rate, spray water mist at the tail to increase the reactivity of calcium oxide and SO2 in the flue gas | The technological process is simpler than the limestone gypsum method, and the investment is smaller | Low desulfurization rate: about 70%, small operating flexibility, high calcium-sulfur ratio, high operating cost, unusable by-products and prone to secondary pollution (decomposition of calcium sulfite) |
| Flue gas circulating fluidized bed desulfurization process | In the fluidized bed, lime powder is added to the flue gas in a certain proportion, so that the lime powder is in a fluidized state in the flue gas and reacts repeatedly to form calcium sulfite. | High calcium utilization rate, no moving parts, low investment | Low desulfurization rate: ≥80%, higher requirements for lime purity, domestic lime is not easy to guarantee quality, flue gas pressure head loss is large, and boiler operation will be affected due to uneven feeding |
| Seawater desulfurization process | Use seawater to wash flue gas to absorb SO2 gas in flue gas | The desulfurization rate is relatively high: ≥90%, the process is simple, the investment is low, the floor area is small, and the operating cost is low | Restricted by geographical conditions, it can only be used in coastal areas. Only suitable for medium and low-sulfur coal types, with secondary pollution |
| Electron beam desulfurization process | Cool the flue gas to about 60°C and irradiate it with electron beams; generate free radicals, generate sulfuric acid and nitric acid, and then react with the added ammonia gas to generate ammonium sulfate and ammonium nitrate. Collect ammonium sulfate and ammonium nitrate powder and granulate to make compound fertilizer | High desulfurization rate: ≥90%, desulfurization and denitrification at the same time, the by-product is an excellent compound fertilizer, no waste generated | The investment is high, because the equipment components are not qualified, it should be more difficult for large-scale units |
| Ammonia washing desulfurization process | Using various concentrations of ammonia (or liquid ammonia) as a desulfurizer, the resulting ammonium sulfate slurry is transported to the concentrated dehydration treatment system | High desulfurization rate: ≥95%; compared with calcium-based desulfurization, the system is simple, the equipment is small in size, and the energy consumption is low; the by-product ammonium sulfate is a common chemical fertilizer; no secondary pollution is generated; desulfurization can remove part of the NOx | Ammonia is easy to volatilize; the equipment is highly corroded and the cost of anticorrosion is high; it is necessary to prevent the generation of aerosols |
| Ammonium Phosphate Fertilizer Flue Gas Desulfurization Process | Let the flue gas pass through the activated carbon with catalyst, the SO2 in the flue gas is catalyzed into SO3 and adsorbed in the activated carbon, the SO3 in the activated carbon is washed with water to become dilute sulfuric acid and the activated carbon is regenerated. | High desulfurization rate: ≥90%, simple process flow, no moving equipment, low investment and low operating costs. | The by-product is dilute sulfuric acid, which is not suitable for transportation and can only be digested locally. Activated carbon needs to be replaced every 5 years. |
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