Wet Flue Gas Desulphurization System Research Articles

Uncertainty and disturbance estimator-based model predictive control for wet flue gas desulphurization system

Uncertainty and disturbance estimator-based model predictive control for wet flue gas desulphurization system

Flexible Control of Wet Desulphurization Process Based on Frequency Retrofit

To assist in the absorption of renewable energy, coal-fired power plants need to operate over a wide range of loads, which exacerbates the challenge of the time delay in the wet desulphurization process. Therefore, this paper proposes a new control structure based on frequency retrofit and a corresponding model predictive controller to change the traditional idea of wet desulphurization control. This structure provides faster control actions, thus reducing time delay directly. And it makes the original discrete control variable continuous, enabling most control methods. The field application to the wet flue gas desulphurization system reveals the practical prospects of the proposed control structure and simulations have been conducted to verify the merits of the proposed control scheme based on data collected from a 1000 MW power plant.

FGD (FLUE GAS DESULPHURIZATION) SYTEM -OVER VIEW

Advantage of using dry FGD (FLUE GAS DESULPHURIZATION) System instead of the WET FGD System in terms of efficiency and cost-effective solution. Though, the high cost of expensive slaked/quick lime required as reagent in dry FGDs, considering the capital cost of the project and considering the Water saving (useful in the water scarcity area) the Dry FGD system shall be recommended.

Analysis of Desulfurization Characteristics in Coal-Fired Power Plant by Numerical Simulation and Computer Simulation

In this paper, the spray tower of a wet flue gas desulphurization system in a coal-fired power plant is studied. The flue gas and slurry droplet are two-way coupled with Euler-Lagrange method. The heat and mass transfer and the ion reaction in SO2 removal are also considered. The results show that the error between simulation removal efficiency and practical value is within 5% under the above models. Adjusting liquid-gas ratio and opening spray layer are beneficial to the SO2 removal, and the optimal liquid-gas ratio is 16 L/m3. Balance gas velocity is needed, because an overlarge velocity will significantly reduce removal efficiency.

Effect of a Wet Flue Gas Desulphurization System on the Emission of PM2.5 from Coal-Fired Power Plants

Wet flue gas desulphurization (WFGD) is wildly used to control SO2 emission from coal-fired power plants. The influence of WFGD on particulate matter (PM) emission has recently drawn significant public attentions in China. In this study, PM2.5 was collected at both the inlet and outlet from three WFGD units, including a single scrubber lime-stone-gypsum FGD unit, a cascade scrubber lime-stone-gypsum FGD unit, and a seawater FGD unit. PM2.5 mass concentrations and their chemical compositions were analyzed. A method to calculate the addition and removal ratios is proposed according to the concertation of PM2.5 components, such as Ti, Pb, Cr, and V. The results indicate that the removal ratio was similar between the three WFGD units (77.1% on average). However, the addition ratio varied significantly. The performance of the cascade scrubber lime-stone-gypsum FGD unit was best, with a lower addition ratio of 8.6%, which is attributed to the weaker evaporation of desulphurization slurry droplets in their second tower under the low temperature of the flue gas. The addition ratio of the seawater FGD unit was also low (23.9%) because of its low concentration of solids in the seawater. The addition ratio of the single scrubber lime-stone-gypsum FGD system was highest, with a value of 162.3%, which was probably due to the low efficiency of the de-mister.

Trace element (Hg, As, Cr, Cd, Pb) distribution and speciation in coal-fired power plants

This work reports the distribution of selected trace elements, including Hg, As, Cr, Cd and Pb, from different sampling locations in a 300MW coal-fired power plant. The plant is equipped with low NOx burners, a selective catalytic reduction (SCR) denitrification system, an electrostatic precipitator (ESP) and a wet flue gas desulphurization system (WFGD). It was found that Cd is approximately evenly distributed between the bottom ash, fly ash and gypsum. Pb, Cr and As are mostly concentrated in the fly ash. Mercury, being the most volatile element, has the lower concentration in the solid form among the five target elements. The concentrations of As, Cr and Pb are higher in fly ash than in the gypsum, in contrast to Hg and Cd. FGD gypsum samples and fly ash samples from four coal-fired power plants were collected. Samples were leached and analyzed for the speciation of trace elements by a five-step extraction procedure modified from the Community Bureau of Reference (BCR) method. The speciation study indicates that more residual fraction for Hg, As and Pb than that of effective fraction in both fly ash and gypsum. However, Cr and Cd have more effective fraction than that of residual fraction in both fly ash and gypsum. In fly ash, 60 to 90% of the trace elements exist in the residual fraction. The stability of trace elements in the gypsum is weaker than that of the fly ash in the environmental resource utilization. This may mean that the trace elements should be retained in the fly ash as much as possible.

Pilot Study on In-depth Water Saving and Heat Recovery from Tail Flue Gas in Lignite-fired Power Plant

In lignite-fired power plants, the high water content of lignite (35-40%) is responsible for significant reductions in boiler efficiency due to the large amounts of heat loss experienced through water evaporation during coal combustion. Installation of a water condensation device in the outlet of the desulfurization absorption tower can recover substantial amounts of water and latent heat from the flue gas that containing saturated steam. In the present study, a pilot test platform was built into a 600MW lignite-fired power plant, and a 50,000m3/h flue gas flow was been extracted and cooled by 5°Cduring the test. Using our theoretical model for this energy efficiency innovation, the test results demonstrate that 129.5GJ/h of latent heat can be recovered and 61.6t/h condensate water can be collected from the flue gas (2,500,000m3/h) for the600MWlignite-fired power plant. The wet flue gas desulphurization system (wet FGD) consumes the supplemental water of 60-80 t/h for this power plant. Consequently, the water recovery quantity of 73 t/h demonstrate that zero net water consumption can be achieved by returning the recovered water back into wet FGD.

Causes Analysis of Wet Flue Gas Desulphurization Stack Rainout for the Thermal Powerplant without GGH and its Countermeasures

This paper introduces the phenomenon of stack rainout in the wet flue gas desulphurization system for the thermal power plant units without GGH,analyzes the factors affecting rainout of wet stack and finds out the main causes resulting in stack rainout of wet flue gas desulphurization for Wangtan Power Plant without GGH,such as low temperature after the flue gas desulfurizationinsufficient diffusion capability of flue gas flowthe blockage of mist eliminatorpoor operation of electrostatic precipitatorinadequate combustion of boilerhigh speed of flue gas flow in the stackthe effect of climate. Also it is analyzed that the mist eliminator equipment and ensuring the efficient operation of electrostatic precipitator may relieve the phenomenon of stack rainout.

Effect of selective catalytic reactor on oxidation and enhanced removal of mercury in coal-fired power plants

The present study investigated the variation of mercury (Hg) speciation within the air pollution control devices (APCDs) in bituminous coal-fired power plants. The effect of selective catalytic reduction (SCR) system, which is mainly installed for NO x removal, on elemental Hg (Hg 0) oxidation and enhancement of Hg removal within APCDs, was studied. Hg speciations in flue gas at the inlet and outlet of each APCDs, such as SCR, cold-side electrostatic precipitator (CS-ESP) and flue gas desulphurization (FGD), were analyzed. Sampling and analysis were carried out according to Ontario Hydro Method (OHM). Overall Hg removal efficiency of APCDs, on average, was about 61% and 47% with and without SCR system, respectively. In the flue gas, Hg was mainly distributed in gaseous (elemental and oxidized) form. The oxidized to elemental Hg partitioning coefficient increased due to oxidation of Hg 0 across the SCR system and decreased due to the removal of oxidized Hg (Hg 2+) across a wet FGD system. Hg 0 oxidation across the SCR system varied from 74% to 7% in tested coal-fired power plants. The comparative study shows that the installation of an SCR system increased Hg removal efficiency and suppressed the reemission of captured Hg 0 within a wet FGD system.

Duplex and Superduplex stainless steel grades for wet flue gas desulphurisation systems

The corrosion risks in a wet flue gas desulphurization system environment are reported. Uniform and localized corrosion resistance of different stainless steels is studied by electrochemical tests. The effects of chloride content, fluoride content, pH and temperature on corrosion resistance are discussed. The results show that duplex UNS S32205 or superduplex UNS S32520 grades are prime substitutes for austenitic 317LNM or super austenitic like UNS S34565 grades in many aggressive environments. The life cycle costs of scrubbers constructed of stainless steels plates or clad plates are compared. The excellent corrosion resistance of duplex and superduplex stainless steels, combined with their increased mechanical properties and moderate alloy cost afford very cost effective solutions for wet flue gas desulphurization.