Wet Desulphurization Research Articles

A case analysis and treatment measures of high moisture content in wet desulphurization gypsum

China’s thermal power plant wet FGD (flue gas desulphurization) produces more than 80 million tons of gypsum each year. The factors affecting the quality of wet desulphurization gypsum are limestone quality, flue gas dust, gypsum slurry pH, slurry quality, gypsum water content, desulphurization system design features, and operating conditions, etc. There are many reasons for high gypsum moisture content, and the analysis and solution are particularly complex. Through a case analysis of a power plant with high moisture content of desulphurization gypsum, the main reasons are that the unit has been operating under low load conditions for a long time with low sulphur coal, limestone supply slurry is high, slurry pH is high, and the volume of gypsum crystals generated is small, resulting in gypsum dehydration difficulty and high moisture content. The measures were to add the crystal seeds into the slurry and to lower the operation pH. The slurry quality is improved, and the gypsum dehydration returns to normal. The design margin of the desulphurization system is large, even in a long-term low sulphur and low load operation. There are no similar cases, and this situation generally does not attract attention. It is worth further analysis and reference.

Thermo-economic analyses of the waste heat and water recovery system from flue gas by heat pump integrated with different heat utilization ways in coal-fired power plant

To recover the waste heat and water simultaneously from flue gas after wet desulphurization, a novel method by adding a flash evaporation device and heat pump system was proposed. The thermal-economic theoretical models for systems integrated with three different heat utilization ways were established based on the method of equivalent enthalpy drop. A typical 300 MW coal-fired power plant was selected as a case to compare the thermo-economic performance. Results show that when the flue gas temperature decreased from 50°C to 30°C, the amounts of recovered waste heat and water could be up to 65.2MW and 81.4t/h, respectively. At the same heat output of 11.3 MW from heat pump, the heat utilization way of pre-heating air exhibited the best energy-saving performance with the net efficiency of power plant increasing to 42.46% from 42.3%.

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.

Comparative study on direct and indirect methods for wet desulphurisation and denitrification based on micro-nano bubbles

ABSTRACT The wet desulphurisation and denitrification technique based on micro-nano bubbles, which is available by either D-method or I-method, is a promising novel process. By employing piped water, Na2SO3 aqueous solution and HA-Na aqueous solution as the absorption liquids, a comparative study was conducted in this article on D-method and I-method to analyze their performance, advantages and disadvantages. It was accompanied by an investigation of how initial pH and initial temperature values of the absorption liquids affected the removal efficiency. The results suggested a positive correlation between NO/SO2 removal efficiencies and pH values but a little improvement in the removal efficiency under alkaline conditions. Furthermore, heating the absorption liquids inhibited the removal of NO and SO2. When manipulated in the same experimental environment, D-method and I-method did not present a significant difference in the SO2 removal efficiency, while the former was remarkably more effective than the latter in removing NO. To put together, D-method had higher removal efficiency, but required a large-scale micro-nano bubble generator to process a large quantity of flue gas as the micro-nano bubble generator was subject to a limited inlet flow rate. Consequently, an increase in investment and operating costs was incurred, while this issue could be avoided by I-method.

Improving the efficiency of fluidized bed comminution of limestone samples

Purpose: The aim of the research was to describe the properties and methods of using limestone for desulfurization of flue gases and to analyse the process of fluidized bed comminution and the influence of selected parameters and stand modification on quality of product of fluidized bed comminution. Design/methodology/approach: Tests of the grinding process on the fluidized bed were carried out using a modified fluid bed mill for operational variable parameters and their results were compared with the results received before modification. The modification of the test stand consisted of increasing the height of the grinding chamber, which ensured an increase in the volume of the fluidized layer where the grinding process takes place. Findings: Main parameters that determined the effects of comminution in the analyzed case were: overpressure of working air and the rotor speed of the classifier. The introduction of the modifications of the test stand ensured an increase in the volume of the fluidized layer in which the grinding process takes place. As well as a greater gravitational classification, which caused larger grains to be stopped in the grinding chamber and shift of characteristics of grain compositions towards finer grains. Research limitations/implications: It is assumed that the diameter of sorbent grains used in the fluidized bed can not exceed 6 mm. The granularity of the offered sorbents ranges from 0.1 mm to 1.2 mm. The quality of the desulfurization process depends on the overall granulation of used sorbent grains. Practical implications: Appropriately selected sorbent grains used in wet and dry flue gas desulphurisation plants ensure improved efficiency of the desulphurisation process and lower operating costs of the installation. Originality/value: Thanks to the comminution method used, a sorbent is obtained without impurities and with an increased specific surface, which can be used in fluidized bed boilers.

Analysis on the Reason of Excessive Moisture Content in Wet FGD System in a Power Plant

In a thermal power plant flue gas wet desulphurization system appeared the problem of high-moisture content of gypsum. The paper combines the desulfurization system operating statement and laboratory analysing results. Meanwhile, it analyses the factors composed high-moisture content. The conclusion shows that there are several main factors influence the gypsum dehydration effect, namely content of dust concentration about the system entrance disposal situation of desulphurization wastewater and the quantity of air oxidation. The paper also shows that the gypsum cyclone running condition directly influences the effect of gypsum slurry dehydration. The paper suggests that,in order to ensure the safe operation of desulphurization system, the correspondent treatment measures and suggestions were put forward.

Causes and treatments of foaming and overflow of calcium-based wet desulphurization slurry

During the operation of the calcium-based wet desulfurization system, slurry foaming and overflow are prone to occur, which is not conducive to the safe and stable operation of the desulfurization system. In order to solve the problem of slurry foaming, the main properties of the slurry were tested by taking the wet flue gas desulfurization device of a sintering machine of a steel company as an example. The foaming ability of the liquid is characterized by its foaming height and defoaming time, and the influence of surface active substances, particles and metal ions in the slurry on its foaming ability has been studied through multiple experiments. Combining the foaming mechanism and the desulfurization process, the cause of the slurry foaming is analyzed, and measures are given to prevent and treat the slurry foaming overflow to ensure the normal operation of the absorption tower.

Effect of steam supply to the air-blown gasifier on hot syngas desulphurization

The IGCC technology serves to efficiently produce thermal and electrical energy with minimal impact on the environment. In operating IGCC, wet desulphurization is used at temperatures below 200°C. The use of hot desulphurization at temperatures around 500°C will significantly improve IGCC efficiency. The preferred sorbent for hot gas cleaning is ZnO. At temperature of 450-500°C, ZnO begins decomposing because of reactions with syngas components (primarily hydrogen). Steam impedes reaction of ZnO with H2 and increases ZnO thermal stability. Syngas H2/H2O ratio is determined by gasifier operation mode. The purpose of this work is to determine maximum temperature of hot gas cleaning depending on condition of ZnO-sorbent thermal stability and steam-air-blown mechanically activated coal gasifier operation mode. To determine the effect of steam supply to syngas composition, experiments were performed on entrained-flow gasifier (1 MW). Experimental results were processed using thermodynamic analysis to determine idealized syngas composition and CFD-modeling to determine real experiment process parameters. Syngas H2O content was determined by CFD-modeling results. Study of ZnO-sorbent thermal stability depending on H2 concentration and syngas H2/H2O ratio was performed by TGA. As a result of experimentally confirmed thermodynamic calculations, ZnO-sorbent thermal stability was found to increase to 815°C due to steam dilution.

Synthetic zeolites as potential sorbents of mercury from wastewater occurring during wet FGD processes of flue gas

This paper evaluates the suitability of fly ash-derived zeolites as sorbents of mercury in water and wastewater. The tested materials were type X and type A synthetic zeolites obtained by hydrothermal synthesis of Class F fly ash. Silver-modified type X fly ash-derived zeolites were also used to check the need for structural modification. The commercial products 4A and 13X zeolites were used as reference materials. Mercury sorption experiments were carried out under static conditions in an artificial solution with an Hg concentration in the range of 13.20–575 mg dm−3. In each case, the sorption efficiency was achieved at a level of above 90%. A second experiment involved the removal of mercury from real wastewater using the wet desulphurization process for flue gas. The results for the tested samples show extremely high sorption efficiency at a level of 99%. Based on these results, it can be stated that fly ash-derived zeolites have similar sorption properties to commercial products in terms of their used as mercury sorbents for liquid waste and are therefore a cost-effective substitute for commercially available products. The X and A types of the zeolite structure were found to remove mercury at a similar level.

Basic rules of NO oxidation by Fe2+/H2O2/AA directional decomposition system

AbstractBasic rules of NO oxidation by a Fe2+/H2O2/AA directional decomposition system were researched based on the technical background of flue gas NOx removal. Effects of gas‐liquid interfacial area, main gas, and solution parameters on NO oxidation efficiency (η) were analyzed. The results showed that adequate contact area was the precondition for high η by a Fe2+/H2O2/AA system. η decreased with the increase in NO concentration, which illustrated that this method would be efficient in oxidizing NO at a low concentration. η tended to decrease linearly with the growth in gas flow, however, the NO oxidation rate (v) rose with the increase in NO concentration and gas flow. η increased with the initial concentrations of H2O2 and Fe2+, but the amplitude decreased. Controlling the initial concentrations of H2O2 and Fe2+ to achieve reasonable synergies between generation rate and consumption rate of ·OH could weaken the invalid consumption of reactants. η increased with the increase in temperature in the range 30–60 °C, but it nearly did not change with temperature after 60 °C. This oxidation technology and the traditional wet flue gas desulphurization technology exhibited temperature synergy. Under typical pH of wet desulphurization, η and H2O2 consumption rate did not change obviously.

Qualitative and quantitative characterization of a coal power plant waste by TG/DSC/MS, XRF and XRD

SO2 removal from coal-fired power plant flue gases can be done by dry, semi-dry or wet desulphurization processes, using limestone or lime-containing products as sorbents. In a Brazilian coal power plant, there is a dry desulphurization unit to capture SO2 with hydrated lime from the combustion gases. A part of the flying ashes produced is mixed with the bottom coal ashes and the spent sulphated product generated after SO2 capture. This residual solid blend is then buried in a non-productive area, from which coal was already extracted and is studied in this work. According to the authors’ experience in the development and characterization of adsorbents for low-temperature dry desulphurization processes and in thermogravimetric analysis, this paper shows and discusses a method which was developed to characterize qualitatively and quantitatively the chemical and mineral composition of this waste by using thermogravimetry coupled with mass spectrometry, X-ray fluorescence and X-ray diffraction, to preview new potential industrial applications for this waste.

Benefit Analysis and FGD Optimization for Designed Power Plant Based on Comprehensive Benefit Index System

Taking the initial design value for target power plant as standard index values, two comprehensive benefit index systems for flue gas desulphurization (FGD) technology were formed by mean square difference method with or without the index of earning of by-product, to analyze the environmental benefit, economic benefit, technology benefit and comprehensive benefit of six flue gas desulphurization technologies on designed power plant and obtained the optimal technology ultimately. For the index system with index of earning of by-product, the optimal FGD technology is wet ammonia desulphurization, not only possesses the biggest comprehensive benefit, but also the biggest economical and technology benefit for designed power plant. For the index system without the index of earning of by-product, the wet ammonia desulphurization, limestone wet desulfurization and simple wet desulfurization have similar comprehensive benefits, but individual advantage on environmental, economic and technology benefit separately.

Efficiency Prediction of Limestone-Gypsum Wet Desulphurization Based on Support Vector Machine

This paper studies the prediction of power plant desulfurization efficiency, based on support vector machine through the meshing method for parameter optimization, establish a prediction model, with the running of the actual data to predict the results: mean square error (MSE) is 0.00259324, the correlation coefficient (R) is 0.979927%, the largest error is less than 1.5%, the results show that the established forecast model based on support vector machine (SVM) with high accuracy to predict the desulfurization efficiency, and can satisfy the engineering need of flue gas desulfurization efficiency prediction.

A comprehensive evaluation of the influence of air combustion and oxy-fuel combustion flue gas constituents on Hg0 re-emission in WFGD systems

This paper evaluates the influence of the main constituents of flue gases from coal combustion (CO2, O2, N2 and water vapor), in air and oxy-fuel combustion conditions on the re-emission of Hg0 in wet scrubbers. It was observed that the concentration of water vapor does not affect the re-emission of mercury, whereas O2 and CO2 have a notable influence. High concentrations of O2 in the flue gas prevent the re-emission of Hg0 due to the reaction of oxygen with the metals present in low oxidation states. High concentrations of CO2, which cause a decrease in the pH and the redox potential of gypsum slurries, reduce the amount of Hg0 that is re-emitted. As a consequence, the high content of CO2 in oxy-fuel combustion may decrease the re-emission of Hg0 due to the solubility of CO2 in the suspension and the decrease in the pH. It was also found that O2 affects the stabilization of Hg2+ species in gypsum slurries. The results of this study confirm that the amount of metals present in limestone as well as the redox potential and pH of the slurries in wet desulphurization plants need to be strictly controlled to reduce Hg0 re-emissions from power plants operating under oxy-fuel combustion conditions.

Analysis of the Causes of High Calcium Carbonate Content in Coal-Fired Power Plant Desulfurization Gypsum

In this paper, the problem of high calcium carbonate content of desulfurization gypsum using limestone - gypsum wet desulphurization technology in coal-fired power plants questions, recommendations in running process from the control of absorption tower pH, lime stone powder, lime powder fineness activity to solve the above problems.

The Problems and Countermeasures of Maintaining Wet Desulphurization in Power Coal-Fired Plant

Based on the study of the maintaining of wet desulphurization installments in coal-fired power plant, similar problems have been found in maintaining process. including desulphurization absorption tower, mist eliminator, slurry circulating pump, gas duct, flue damper. The corresponding countermeasures have been proposed.

Mathematical Simulation of Membrane-Absorption for H<sub>2</sub>S Capture from Nature Gas

A dynamic model of mass transfer was developed with mass transfer equation and mass transfer differential equation according to two film theory for the simultaneous transport of hydrogen sulfide through hollow fiber membrane (HFM) contactors while using N-methyldiethanolamine (MDEA) as the chemical solvent. The model results are in excellent agreement with the experimental data. The results indicate that the removal of H2S increased while increasing concentration of MDEA and gas pressure, however, the removal of H2S decreases while increasing gas velocity. The concentration of H2S increases at the same place in the lumen while increasing gas velocity. There is serious decreasing amplitude of axial concentration of H2S during the initial stage, but it slows down at half of the length and a great reduction of H2S concentration in radial direction with the increase of the length. The decreasing amplitude is dropped due to the concentration of H2S decreased in radial direction. The model can indicate H2S removal rate in given operational conditions and offer theory evidence for the design of membrane contactor. Natural gas is believed to play a vital role in the next few decades for industrial and domestic utilization. It is considered as one of the cleanest and safest of all energy sources. However, nature gas is not a pure hydrocarbon and sometimes it has some sour gases such as hydrogen sulfide which has high toxicity. Hydrogen sulfide can not only corrode equipment and transmission pipeline under aerobic and hot humid conditions but also cause catalyst poisoning, even serious threaten the safety of human. Wet desulphurization is widely used for natural gas treatment and aqueous solutions of alkanolamines are often used as absorption solvent. Among these alkanolamines, MDEA as an absorption solvent of acid gases is widely used today because it possesses the characteristics such as higher H2S selectivity, bigger absorption capacity, lower regeneration energy, smaller hot-degradation and lower circulating load. But desulphurization unit can be seriously corroded in the sulfur removal process. On the other hand, these conventional processes such as absorption towers, packed and plate columns possess many disadvantages such as flooding, foam formation, and demand high capital and operating costs. So the technology meets a certain obstacles. Recently, new processes using gas–liquid membrane contactors as gas absorption devices have been a subject of great interest. Among the diversity of membrane geometries available for membrane contactors, hollow-fiber membrane contactors are favored due to their high surface/volume ratio for separation which is 30-50 times compared with traditional absorbers. This type of process offers several practical advantages including low energy and operating costs, simplicity and occupying small area. In addition, membrane contactors as unit equipment can be combined according to actual need. [4~5] used polypropylene hollow fiber membrane as the absorber and MDEA as the chemical solvent for the absorption of H2S via changing operating conditions (e.g. temperature, pressure, the concentration of the solvent, flux of gas-liquid phase) and studied the influence of the changes to mass transfer coefficient and sulfur removal efficiency. The results indicate that the sulfur removal efficiency can be 95% above by optimizing the operating conditions. At home and abroad, comprehensive two-dimensional mathematical models were developed based on differential equation. Wang [6] simulated the absorption of CO2 using different absorption medium in hollow fiber membrane contactors. But they did not consider the effect of mixed gas. Chen [7] modeled the distribution of reactants and products concentration in the shell side in different typ es of reaction. However, the model can not obtain the concentration of H2S in the lumen. Rami Faiz [8] modeled the distribution of acid gas, but the mathematical model was not validated by the experimental work.

Cause Analysis and Countermeasure of Gypsum Rain in Coal-fired Power Plants

Focusing on the phenomenon of gypsum rain while wet desulphurization(WFGD) were adopted in coal fired power plant without GGH, the paper studied and put forward the solutions : (1) desulfurization facilities related equipment modification; (2) optimal operation of existing desulfurization facilities.

Study on Sintering Red Mud Desulphurization Characteristics in Liquid-Column Impingement Scrubber

The feasibility of sintering red mud as wet desulphurization sorbent was studied in this paper. The comparative study of desulphurization efficiency by using sintering red mud and traditional desulphurization sorbent-limestone had done in Liquid-column impingement Scrubber apparatus. The effects of gas velocity, liquid-gas ratio and pH value on desulphurization efficiency were studied. Results show that the desulphurization efficiency of sintering red mud is lower than that of limestone in the same slurry mass concentration, while the sintering red mud can be used as desulphurization sorbent when increase its slurry solid content in appropriate way. The gas and droplets can mix well in absorption section when the gas velocity is upper than 2.7m/s. The desulphurization efficiency higher than 80% can be obtained when L/G ratio higher than 15L/m3 and the pH values between 5.2- 7.

Experimental Study on Internal Flow Field of Wet Desulphurization Tower

In order to study the flue gas velocity distribution and pressure drop characteristics inside wet desulfurization Tower, experimental study has been carried out. Flow model is built with geometric scale of 1 / 12 , flue gas velocity ratio of 1 / 1 and different gas entrance angle as 12°and 7°. Experiment result shows that Spray liquid droplets made gas more evenly; The evenness of gas velocity distribution is very poor with very low gas load (<35%);The pressure drop in tower increases with increase of sprayer and increases with increase of gas load; The evenness of gas velocity distribution becomes poor and the pressure drop increases when gas inlet angle changes from 12°to 7°.