This paper analyzed the energy consumption characteristics of typical limestone-gypsum wet flue gas desulfurization (FGD) system which is widely used in power plant for SO x removal, and discussed its optimal operation. In the FGD system, booster fan; circulating slurry pump and oxidation fan are three major energy consuming devices. We established the mathematical models to disclose the relationship between the energy consumption and the desulfurization features of these equipments. On this basis, we obtained the performance curve of these equipments and proposed the optimal operation ways of the FGD system. The promising results obtained here provide a new approach for desulfurization with low energy consumption.

Through experiments on desulfurization, CaSO 4 decomposition, and system approach using theoretical analysis, the in-furnace desulfurization in an O 2 /CO 2 combustion system with partial CO 2 removal from recycled gas was investigated. The results revealed that the SO 2 concentration increased with the CO 2 removal ratio and could be much higher than conventional combustion in air. This high SO 2 concentration came from the enrichment effect of gas recirculation, at a high gas recirculation ratio of 0.989. The system desulfurization efficiency also increased with the CO 2 removal ratio. Under the conditions investigated, the system efficiency of in-furnace desulfurization could be as high as 88.5%. The system desulfurization efficiency for the new scheme could be 6−10 times higher than conventional combustion in air. With this new scheme, easy CO 2 recovery and efficient in-furnace desulfurization could be realized simultaneously.

A new scheme of oxyfuel combustion combined with partial removal of CO 2 from recycled gas and MILD combustion was proposed. Through experiments and theoretical analysis including the Monte Carlo method, the characteristics of in-furnace desulfurization in this new scheme was investigated. It was found that as the initial O 2 concentration decreased, the gas recirculation ratio, SO 2 concentration, and global efficiency of in-furnace desulfurization increased. On the other hand, the gas recirculation ratio, SO 2 concentration, and global efficiency of in-furnace desulfurization increased as the CO 2 removal ratio increased. The practical residence time of SO 2 in oxyfuel-MILD coal combustion increased to about five to thirteen times as long as that of conventional pulverized coal combustion. The contributions of oxyfuel combustion, partial removal of CO 2 from recycled gas, and MILD combustion, to the high desulfurization efficiency, were almost the same importance. At CO 2 removal ratio = 11% and initial O 2 concentration = 16%, the gas recirculation ratio became as high as 99.12%, i.e., only 0.88% of the flue gas was exhausted to the atmosphere. The corresponding system desulfurization efficiency was as high as 95.8%. It was demonstrated that this new scheme can realize extremely high in-furnace desulfurization efficiency in addition to easy CO 2 recovery.

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Abstract:The influence of loading strategies on combustion and emissions parameters is experimentally and numerically studied under typical 5 s transient conditions of constant speed and increasing torque. The experiment is conducted on a two-stage turbocharged heavy-duty diesel engine with a constant opening valve high-pressure exhaust gas recirculation (EGR) system. The test results show that: compared with the full-stage loading (FSL) strategy (constant loading rate during the entire transient process), the sectional-stage loading (SSL) strategies (holding a certain time at 50% load) can significantly reduce soot emissions (by 41.3%); the greater the first-stage loading rate, the better the torque response performance, which maximally increases by 56.7%. Besides, longer loading holding time can effectively restrain the overshoot of EGR rate and advance the combustion phase (CA10, CA50) at medium and large loads. However, the larger second-stage loading rate slightly deteriorates the combustion and emission performance. This deterioration situation can be markedly suppressed by adopting a suitable loading hold time.

A new scheme of O 2 /CO 2 combustion with partial CO 2 removal from recycled gas is proposed. Through experiments and theoretical analysis of the system, the reduction of NO to N 2 and emission of NO were investigated for this new scheme. When CO 2 is partially removed from the recycled gas, a high gas recirculation ratio is needed to maintain the O 2 concentration at the furnace entrance and the stoichiometric O 2 amount necessary for the burn-out of coal. It was found that this gas recirculation ratio increased with the CO 2 removal ratio from the recycled gas. The gas recirculation ratio could be as high as 98.9%; i.e., only 1.1% of the flue gas was exhausted. The CO 2 concentration in the flue gas was above 95%, which made its capture much easier and more economical. The global conversion ratio from fuel N to exhausted NO decreased as the CO 2 removal ratio from the recycled gas increased. At a CO 2 removal ratio of 15%, the global conversion ratio from fuel N to exhausted NO became as low as 3.95 × 10 −3 , i.e., down to only 1 / 85 of that of conventional combustion in air. These results suggested that, with the new scheme of O 2 /CO 2 combustion proposed in this work, superlow NO emission and easy CO 2 capture could be realized simultaneously.

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Theoretical model for calculating the outlet flue gas temperature of limestone-gypsum wet flue gas desulfurization (FGD) absorption tower is important for water consumption calculation. In this paper, the energy balance in the spray zone is analyzed and a model for calculating the outlet flue gas temperature of FGD absorption tower is proposed. An example computation of the outlet flue gas temperature of a typical 600MW class unit’s operation data is introduced, the result has verified the model. A further study of significance analysis has then been made to analyze and simplify the model.