Boiler Flue Gas Research Articles

Theoretical and experimental study on total heat recovery of condensing gas boiler flue gas by gas engine-driven compression heat pump

How to improve the utilization efficiency of natural gas and achieve the goal of carbon reduction has gradually become the focus of people’s attention. The exhaust temperature of the condensing gas boiler is between 50℃ and 80℃, which still contains some heat that is not used, so it is necessary to recover this part of the heat. This paper mainly studies the total heat recovery and utilization of waste heat from low-temperature flue gas of condensing gas boiler. In the research field of gas boiler flue gas waste heat recovery, the use of gas compression heat pump to recover gas boiler flue gas waste heat is still very few. Based on the principle of reducing the cold source temperature, a low-temperature flue gas recovery scheme of a gas engine-driven compression heat pump coupled condensing gas boiler is proposed. The low-temperature chilled water produced by gas engine-driven compression heat pump is used to recover flue gas waste heat from condensing gas boiler and gas engine, which can improve the utilization efficiency of natural gas and eliminate the “white smoke phenomenon” simultaneously. In addition, the waste heat of flue gas is used as the low-temperature heat source of gas engine-driven compression heat pump to ensure the stable operation of the heat pump in the low-temperature environment. The flue gas waste heat recovery technology has been improved compared with other flue gas waste heat recovery technologies in terms of primary energy utilization efficiency, system stability, corrosion resistance of flue gas heat exchangers, and investment recovery cycle. The experimental results show that when the water inlet temperature of the flue gas heat exchanger is 15℃, the overall power of the unit can reach 645 kW, and the final exhaust temperature is below 25℃. The overall primary energy utilization rate of the GEHP&CB can reach 110 %, which is 10 %∼20 % higher than that of the condensing gas boiler. The payback period of the increased initial investment is 1.4 heating seasons. Due to the improvement of natural gas utilization efficiency significantly reduces natural gas consumption and pollutant discharge.

A Hybrid Soft Sensor Model for Measuring the Oxygen Content in Boiler Flue Gas.

As an indispensable component of coal-fired power plants, boilers play a crucial role in converting water into high-pressure steam. The oxygen content in the flue gas is a crucial indicator, which indicates the state of combustion within the boiler. The oxygen content not only affects the thermal efficiency of the boiler and the energy utilization of the generator unit, but also has adverse impacts on the environment. Therefore, accurate measurement of the flue gas's oxygen content is of paramount importance in enhancing the energy utilization efficiency of coal-fired power plants and reducing the emissions of waste gas and pollutants. This study proposes a prediction model for the oxygen content in the flue gas that combines the whale optimization algorithm (WOA) and long short-term memory (LSTM) networks. Among them, the whale optimization algorithm (WOA) was used to optimize the learning rate, the number of hidden layers, and the regularization coefficients of the long short-term memory (LSTM). The data used in this study were obtained from a 350 MW power generation unit in a coal-fired power plant to validate the practicality and effectiveness of the proposed hybrid model. The simulation results demonstrated that the whale optimization algorithm-long short-term memory (WOA-LSTM) model achieved an MAE of 0.16493, an RMSE of 0.12712, an MAPE of 2.2254%, and an R2 value of 0.98664. The whale optimization algorithm-long short-term memory (WOA-LSTM) model demonstrated enhancements in accuracy compared with the least squares support vector machine (LSSVM), long short-term memory (LSTM), particle swarm optimization-least squares support vector machine (PSO-LSSVM), and particle swarm optimization-long short-term memory (PSO-LSTM), with improvements of 4.93%, 4.03%, 1.35%, and 0.49%, respectively. These results indicated that the proposed soft sensor model exhibited more accurate performance, which can meet practical requirements of coal-fired power plants.

Multi-objective optimization of the organic Rankine cycle cascade refrigeration cycle driven by sugar mills waste heat

The research on the recovery of low-grade thermal energy carried away by boiler flue gas is significant for sugar mills. This paper designs a waste heat recovery system based on sugar plant flue gas, integrating absorption refrigeration cycle and the organic Rankine cycle, and the effects of nine working fluids on the system are investigated. The aim is to realize the multi-form conversion of energy. The performance of the system is evaluated in terms of energy, exergy, and economic metrics. Multi-objective optimization is performed with the method of the NSGA-II genetic algorithm. The results show that Butane is the most suitable working fluid for ORC. The exergy efficiency of the system is 32.125% before optimisation, with an increased space cooling capacity of 15820.56 MW per year for the sugar mill. The exergy destruction analysis of the system reveals that the generator accounts for the highest proportion of exergy destruction (50.8%). The entire system shows the LCOE is as low as 0.0406$/kWh under the optimized condition. The optimized system can obtain an estimated annual electricity sales revenue of $136,300, and the sugar mill can save $308,600 in cooling costs. In addition, the payback period can be shortened to 5.79 years.

Effect of steam quality on the oil recovery factor of the Karazhanbas field

Background: The injection of the thermal agent as "steam" reduces the viscosity of the oil and the mobility ratio, which increases the displacement and coverage factor, and ultimately significantly increases the oil recovery factor. This statement was the basis for determining the effect of steam enthalpy on the oil recovery factor, as well as for reliably determining the flow rate of flared gas, as a result of which the existing gas pipeline will be reconstructed, the required amount of fresh water will be calculated, and the distribution of steam pumping in the entire Karazhanbas field.
 Aim: The purpose of the article is to consider the influence of the quality of steam produced at the steam generator units of the Karazhanbas field on the oil recovery factor. The main parameter that determines the quality of steam is dryness, which was calculated using the actual values of the boiler (pressure, temperature, gas flow), flue gas tests on a special device, as well as laboratory tests to determine the heat value of the combusted gas.
 Materials and methods: This work used materials from GHM (geological and hydrodynamic modeling), results of studies of boiler flue gases and heat balance.
 Results: The calculation showed a low quality of the produced steam, which negatively affects the recovery factor.
 Conclusion: Evaluation to determine the optimal value of saturated steam parameters (steam dryness, temperature in terms of development efficiency) showed that the higher the temperature and dryness of steam at the wellhead and bottom hole of the injection well, the higher the oil recovery factor at the Karazhanbas field.

Optimizing the CO2 capture and removal process to recover energy and CO2 from the flue gas of boilers and gas turbines outlet with considering the techno-economic analysis

This research aims to evaluate, simulate, and model the CO2 capture process for removing CO2 from the flue gas outlet flow of boilers and gas turbines. To the best of the knowledge Aspen HYSYS was employed to simulate these processes, enabling the analysis of technical conditions and evaluation of the problems and advantages associated with various designs from a technical perspective. Additionally, Aspen Capital Cost Estimator (ICARUS) was utilized for economic analysis.Initially, the CO2 capture process was examined for the removal of CO2 in the flue gas outlet flows of gas turbines and boilers. Subsequently, the process was simulated in the software to explore different optimal modes. Moreover, the feasibility of using a compressor, blower, ejector, and a combination of ejector and compressor was considered so as to provide the necessary pressure for absorption. Finally, the optimal design was selected, and more detailed studies were conducted on its absorption process, taking into account major variables. Among the important factors affecting absorption, were the number of trays, diameter, height, the amount of inlet gas and amine flow rate entering from the top of the tower, as well as the inlet gas pressure.

Design and Characterization of Flue Gas Waste Heat Power Generation Plant

This paper proposes a waste heat recovery system based on temperature difference power generation, which aims to utilize the residual heat in the exhaust flue of chimneys or kilns. The system consists of three parts such as heat collection module, semiconductor power generator, and heat dissipation module, and the residual heat is directly converted into electrical energy and output by temperature difference power generation. The voltage and resistance are measured and analyzed on this basis. This design realizes the waste heat recovery of boiler flue gas, prevents a large amount of waste heat from being discharged into the environment, reduces the greenhouse effect and makes secondary use of the waste heat.

Prediction Modeling of Flue Gas Control for Combustion Efficiency Optimization for Steel Mill Power Plant Boilers Based on Partial Least Squares Regression (PLSR)

The energy-intensive steel industry, which consumes substantial amounts of electricity, meets its power demands through external electricity purchases and self-generation through the operation of its own generators. This study aimed to optimize boiler combustion efficiency and increase power generation output by deriving optimal operational values for O2 and CO within the boiler flue gas using machine learning (ML) with the aim of achieving maximum boiler efficiency. This study focuses on the power-generation boilers at steel mill P in Korea. First, 361 types of operation data from power generation equipment were collected and preprocessed. Subsequently, a partial least squares regression (PLSR) algorithm was used to develop a prediction model for O2 and CO values, known as the Boiler Flue Gas Prediction Model (BFG-PM). The prediction accuracy for O2 was notably high (83.2%), whereas that for CO was lower (53.4%). Nonetheless, the model’s reliability was high because more than 90% of the predicted values were within a 10% error range. Finally, the correlation of the BFG-PM model was applied to the performance test code (PTC) 4.0 for the boiler efficiency calculations formula, deriving the optimal O2 and CO control points. Through a simulation, it was verified that the boiler efficiency was improved by controlling the combustion air. In addition, an average increase in boiler efficiency of 0.29% was confirmed by applying it directly to the generator operating on-site. The results of this study are expected to contribute to annual cost savings, with a reduction of USD 217,000 in electricity purchasing costs and USD 19,700 in greenhouse gas emissions trading expenses.

Natural gas-hydrogen hybrid combustion retrofit method and practice for F-class heavy-duty combustion engines

In order to reduce carbon emissions, enhance the operational flexibility of gas turbine power plants, and fill the gap in practical engineering transformation of natural gas-hydrogen blended combustion in heavy-duty gas turbines, a hydrogen blending retrofit was conducted on an F-class heavy-duty gas turbine combined heat and power unit. This served to examine the problems of combustion chamber tempering, combustion pulsation, and NOx emission increase caused by direct hydrogen-doped combustion in the combustion chamber. In this paper, the gas turbine body and hydrogen mixing system were reformed respectively. Retrofit schemes were proposed that were suitable for two operating conditions: 5%–15% and 15%–30% hydrogen blending. Experimental tests were conducted as a means of evaluating the performance of the retrofitted gas turbine and its compatibility with the boiler and steam turbine. The results of the retrofit showed there to be stable combustion, and there was no significant increase in average burner temperatures or occurrence of flashback. The gas turbine power output mostly remained unchanged and NOx emissions met the regulatory standards. The waste heat boiler flue gas temperature was controlled within the range of 84.9–88.2 °C, meaning that the safe operation of the steam turbine was not affected. The hydrogen blending rate was 0.2 Vol%/s, which indicates a smooth and precise control of the hydrogen blending process. It was estimated that the annual reduction in CO2 emissions would be 11,000 tons and 28,400 tons following respective hydrogen blending at 15% and 30%. A reliable retrofit scheme for hydrogen blending in gas turbines based on practical engineering transformation is presented in this study, which has significant reference value.

Design of the Optimum Heat Pipe Heat Exchanger to Recover Heat From Flue Gas of Boiler in case of Chiang Mai Orchid Hotel, Thailand

This study aims to design the optimum heat pipe heat exchanger (HPHE) to recover heat from flue gas of boiler for increasing the temperature of feed water. The optimum thermosyphon heat exchanger sizing was simulated on the basis of thermo-economical method and simulation program was construct by using the MATLAB 2021b. The program was simulated by input physical parameters of the thermosyphon and heat exchanger and the thermoeconomic parameters. It was found that R134a was chosen as the working fluid of this study. In addition, the optimum of number of tubes, heat transfer rate and the optimized effectiveness of HPHE were 87 tubes, 4,873 W and 0.237, respectively. Moreover, the net saving and payback period of this HPHE were 14,865 USD and 310 days, respectively.

Performance of Regenerative Air Preheater of Pulverized Coal Fired Boilers

Abstract: The air preheater (APH) is the final heat trap in the boiler's flue gas path. Effective pre-combustion coal drying and efficient combustion in the boiler are required for APH to operate efficiently. The effectiveness of heat transfer in APH is significantly influenced by the characteristics of relative humidity and ambient air temperature (AAT). Relative humidity (RH) and air density are also impacted by variations in AAT, which in turn alters the heat capacity of the air. If there is insufficient reserve heat exchange capacity in APH, an increase in AAT will diminish the possibility of waste heat recovery. Additionally, a change in AAT will affect the power consumption of the fans and the leakage through various seals.

Alternative alkali activator from pulp mill waste – One-part blast furnace slag mortar activated with recovery boiler fly ash

Alternative alkali activators are a growing research area in the field of alkali-activated materials (AAMs) because conventional chemical-based activators, such as sodium hydroxide and sodium silicate, have a large environmental footprint and high costs. Industrial residues are widely studied as substitutional cementitious materials in concrete and precursors in AAMs but not much as activators. In the present study, sodium rich waste from pulp mill was used as an alkali source in AAMs. Recovery boiler fly ash (RBA) is dust-like waste fraction removed from flue gases of recovery boiler by electrostatic precipitators. It consists mainly of alkalis, sulfate, and carbon while sodium sulfate is the main phase. This work utilized RBA as a sole one-part alkali activator for a precursor mixture containing 95 wt% of blast furnace slag and 5 wt% of cement, and the results were compared with two references, one without activator and the other activated with commercial sodium sulfate. The setting properties and strength gain were comparable between the RBA-activated and commercial activator-activated samples. Calorimetry data showed also similar reactivity between them, and X-ray diffractometry, thermogravimetric analysis, and scanning electron microscopy measurements revealed that the same phases were formed. The main issue was the microcracking of the paste samples when using RBA as an activator. Results confirm the earlier findings from the literature, the activator dosage did not greatly impact the properties: in this study, the initial proportion of 1% or 3% Na2O was the most suitable.

Mass emissions of polycyclic aromatic hydrocarbons during fuel combustion in thermal power plant boilers

RELEVANCE of this study lies in the establishment of technological indicators of emissions of benz(a)pyrene into the atmosphere to assess the degree of negative impact of energy enterprises on the environment and the development on this basis of primary (air protection) measures, inventory of emissions ofpollutants, collection and preparation of initial environmental information for the effective implementation of the principles of technological regulation of emissions in the domestic thermal power industry. THE PURPOSE. The technological features of the formation of polycyclic aromatic hydrocarbons, in particular benz(a)pyrene, in the furnaces of power boilers burning organic fuel are considered. The regime factors significantly influencing the intensity of the formation of benz(a)pyrene as the most carcinogenic and mutagenic impurity influe gases have been determined. As part of the implementation of the principles of technological rationing of polluting marker substances, energy enterprises should determine the mass emission of highly toxic combustion products to improve the environmental performance of combustion processes and establish technological emission indicators. METHODS. Determination of mass emissions of polycyclic aromatic hydrocarbons was carried out using methods of mathematical statistics, processing of environmental information, system analysis of data and processing of the results obtained. RESULTS. Analytical expressions have been developed to determine the content of benz(a)pyrene in the combustion products of coal and anthracite. The values of mass emissions of benz(a)pyrene for inventory and justification of technological rationing of carcinogenic and mutagenic substances at energy enterprises have been determined. CONCLUSION. The results obtained are recommended to be used for a preliminary assessment of the content of benz(a)pyrene in the flue gases of boilers at power plants at the stage of collecting and preparing information for the introduction of technological rationing of highly toxic substances and the assessment of technological emission indicators.

Mechanism of sulfur migration and conversion in pyrolysis/combustion staged conversion process of high sulfur coal

To investigate the effects of circulating ash heat carriers and dolomite catalysts on sulfur migration in the coal pyrolysis/circulating fluidized bed combustion staged conversion process, five experiments of coal pyrolysis, ash/coal co-pyrolysis, coal pyrolysis catalyzed by dolomite, ash/coal co-pyrolysis catalyzed by dolomite and combustion of pyrolysis solid products were designed and carried out. By examining the effects of pyrolysis temperature, heating rate, coal-ash ratio and dolomite species on sulfur migration, the final distribution of sulfur-containing pollutants throughout the staged conversion process was systematically analyzed. The results showed that the separate mixing of ash heat carrier at final pyrolysis temperature of 600 °C increased the residual sulfur in solid phase from 79.29 % of raw coal pyrolysis to 90.00 %. When dolomite catalyst was added individually, the sulfur released into gas phase and tar was reduced from 18.28 % and 2.43 % of the raw coal to 13.14 % and 1.94 %, respectively. And Fe additive significantly improved sulfur resistance of the dolomite catalyst. The regeneration process has little effect on the sulfur fixation capacity of natural dolomite. When ash heat carrier and dolomite catalyst were simultaneously added to the system, the sulfur fixed in ash increased from 79.29 % of the raw coal to 91.27 %, and the sulfur fixed in natural dolomite and modified dolomite accounted for 4.32 % and 4.46 % of the total sulfur, respectively. In the combustion experiments of pyrolysis solid phase products, 43.57 %, 65.57 % and 61.44 % of sulfur was retained in the solid phase residue after combustion with circulating ash, circulating ash/natural dolomite and circulating ash/modified dolomite were added, respectively. Compared with direct combustion of coal, the staged conversion process resulted in a 55 % reduction of sulfur in the boiler flue gas. This study provides a theoretical basis for the purification of sulfur-containing pollutants in the staged conversion process.

Catalytic Oxidation Activity of NO over Mullite-Supported Amorphous Manganese Oxide Catalyst.

Nitric oxide (NO) can pose a severe threat to human health and the environment. Many catalytic materials that contain noble metals can oxidize NO into NO2. Therefore, the development of a low-cost, earth-abundant, and high-performance catalytic material is essential for NO removal. In this study, mullite whiskers on a micro-scale spherical aggregate support were obtained from high-alumina coal fly ash using an acid-alkali combined extraction method. Microspherical aggregates and Mn(NO3)2 were used as the catalyst support and the precursor, respectively. A mullite-supported amorphous manganese oxide (MSAMO) catalyst was prepared by impregnation and calcination at low temperatures, in which amorphous MnOx is evenly dispersed on the surface and inside of aggregated microsphere support. The MSAMO catalyst, with a hierarchical porous structure, exhibits high catalytic performance for the oxidation of NO. The MSAMO catalyst, with a 5 wt% MnOx loading, presented satisfactory NO catalytic oxidation activity at 250 °C, with an NO conversion rate as high as 88%. Manganese exists in a mixed-valence state in amorphous MnOx, and Mn4+ provides the main active sites. The lattice oxygen and chemisorbed oxygen in amorphous MnOx participate in the catalytic oxidation of NO into NO2. This study provides insights into the effectiveness of catalytic NO removal in practical industrial coal-fired boiler flue gas. The development of high-performance MSAMO catalysts represents an important step towards the production of low-cost, earth-abundant, and easily synthesized catalytic oxidation materials.

Design and Research of Thermoelectric Generator Simulation System for Boiler Flue Gas Waste Heat

One of the significant factors contributing to high energy consumption is the unutilized waste heat from flue gas in industrial boilers. Thermoelectric generator (TEG) technology can directly convert thermal energy into electrical energy, and has been gradually applied in the field of waste heat recovery due to its simple and reliable structure, environmental protection, and other advantages. In this paper, a thermoelectric generator simulation system of boiler flue gas waste heat is proposed. The experimental platform is designed by simulating the flue gas waste heat temperature condition of boiler, and the structure of cold end module and hot end module is optimized. During the experiment, the fixed temperature difference was set at 120 °C (hot end:150 °C~cold end: 30 °C). An analysis is conducted on the volt-ampere characteristics and output power of the TEG module. The output characteristics of the TEG system are analyzed under the conditions of variable load, constant load, different pump speed, different heat dissipation modes, and series and parallel connection method. The results show that the experimental platform can instantaneously and accurately test the output parameters of the TEG system, and ensure the intended design requirements. When the ratio of the load resistance to the internal resistance of the TEG module is approximately 1–1.15, the output power of the system reaches its maximum. In order to optimize the output power of the TEG system, a power prediction-based adaptive variable step size maximum power point tracking (MPPT) algorithm is introduced. Additionally, a corresponding mathematical model is formulated. Simulations demonstrate that the time of the improved algorithm to reach the stable maximum power point is 1.54 s faster than that of the traditional algorithm. The improved MPPT algorithm satisfies the criteria for speed and accuracy, diminishes superfluous energy waste, and enhances the overall system efficiency. The research results have certain guiding significance for the design and application of subsequent TEG system.

Recovery boiler back-end heat recovery

Sustainability and efficient use of resources are becoming increasingly important aspects in the operation of all industries. Recently, some biomass-fired boilers have been equipped with increasingly complex condensing back-end heat recovery solutions, sometimes also using heat pumps to upgrade the low-grade heat. In kraft recovery boilers, however, scrubbers are still mainly for gas cleaning, with only simple heat recovery solutions. In this paper, we use process simulation software to study the potential to improve the power generation and energy efficiency by applying condensing back-end heat recovery on a recovery boiler. Different configurations are considered, including heat pumps. Potential streams to serve as heat sinks are considered and evaluated. Lowering the recovery boiler flue gas temperature to approximately 65°C significantly decreases the flue gas losses. The heat can be recovered as hot water, which is used to partially replace low-pressure (LP) steam, making more steam available for the condensing steam turbine portion for increased power generation. The results indicate that in a simple condensing plant, some 1%–4% additional electricity could be generated. In a Nordic mill that provides district heating, even more additional electricity generation, up to 6%, could be achieved. Provided the availability of sufficient low-temperature heat sinks to use the recovered heat, as well as sufficient condensing turbine swallowing capacity to utilize the LP steam, the use of scrubbing and possibly upgrading the heat using heat pumps appears potentially useful.

Prediction of Oxygen Content in Boiler Flue Gas Based on a Convolutional Neural Network

As one of the core pieces of equipment of the thermal power generation system, the economic and environmental performance of a boiler determines the energy efficiency of the thermal power generation unit. The oxygen content in boiler flue gas is an important parameter reflecting the combustion status of the furnace, and accurate prediction of flue gas oxygen content is of great significance for online boiler optimization. In order to solve the online prediction problem of the oxygen content in boiler flue gas, a CNN is applied to build a time series prediction model, which takes the time series samples within a fixed time window as the input of the model and uses several feature extraction modules containing convolutional, activation, and pooling layers for feature extraction and compression, and the model output is the oxygen content in boiler flue gas. Since the oxygen content in boiler flue gas is not only correlated with other variables but also influenced by its own historical trend, the input of the CNN model is improved, and an oxygen content in boiler flue gas time series prediction model (TS-CNN) is established, which takes the historical values of the boiler flue gas oxygen content as the input of the model. The comparison test results show that the R2 and RMSE of the TS-CNN model are 0.8929 and 0.1684, respectively. The prediction accuracy is higher than the CNN model, LSSVM model, and BPNN model by 18.6%, 31.2%, and 54.6%, respectively.

Hydrogen sulfide measurement of combustion gaseous product using ultraviolet absorption spectroscopy

Measurement of hydrogen sulfide (H2S) in gaseous product can provide direct reference for high-temperature corrosion of industrial combustion equipment. Aiming at the interference effect of overlapping measurement of absorption spectrum for H2S and other combustion gas components in UV absorption spectroscopy, the simulation calculation of ultraviolet band absorption spectrum of the typical gaseous products of coal combustion were carried out. The cross interference effects of combustion gaseous products were analyzed in detail. Due to the SO2 and H2S gas under typical combustion condition have equivalent absorption strength in the 228 nm-233 nm band, the influence of SO2 on H2S concentration inversion must be emphatically considered, and the inversion algorithm of H2S gas concentration under the background interference of combustion gaseous products SO2 was put forward. In order to validate the measurement accuracy by the inversion algorithm, the measurement experiments of gas mixture of H2S and SO2 were carried out. The results show that the algorithm can effectively solve the problem of cross interference between the detection of H2S and SO2 in the combustion gaseous products by UV absorption spectroscopy. On this basis, the sampling, pre-treatment and H2S gas concentration measurement system for boiler flue gas near the wall was developed and applied to measure H2S concentration of flue gas near the wall in a 1000 MW ultra-supercritical coal-fired power generation boiler. The results can provide important references for combustion adjustment and high-temperature corrosion prevention of boiler.

Parametric and economic analysis of condensing heat exchanger combined with organic rankine cycle for heat and water recovery from boiler flue gas

This study concerns with heat and water recovery from the flue gas of a natural gas-fired thermal power plant. A combined system of condensing heat exchanger (CHE) and Organic Rankine Cycle (ORC) is proposed. The CHE acts as the super-heater of the ORC. The flue gas enters to the CHE with a temperature of 160 [Formula: see text] and is cooled to under the water vapor dew point temperature and leads to water vapor condensation, therefore latent and sensible heat are recovered. The condensed water is used as cooling tower make-up water. The ORC refrigerant enters to the CHE as a saturated vapor and is superheated by the recovered heat. In order to achieve the best ORC performance and highest water recovery simultaneously, parametric analysis was done in terms of evaporator and superheating temperature. It was found that by increasing evaporator and superheating temperature, the efficiency and generated power of the ORC increase, although water recovery decreases. Also an increase in evaporator and superheating temperature raises the heat transfer area of CHE, particularly in the non-condensing zone. Therefore to find the optimum evaporation temperature an economic analysis based on NPV method was done and 43°C was determined as the optimum evaporation temperature. Considering this condition, flue gas enters the CHE with a temperature of 160°C and leaves it with a temperature of 57.85°C, and on the other side, the refrigerant enters it in a saturated state and leaves it with a temperature of 75°C. The total area of the CHE is about 39,490 m2. The amount of recovered water is 36.78 kg/s, which saves 34.2 % of the make-up water consumption. Also, the production power of the ORC-CHE was calculated as 24.12 MW and the additional power produced by ORC-CHE compared with bare ORC is 3.97 MW.

Influence and mechanism of the adsorption and reactions of residual NH3, NO, and O2 on coal ash after the selective noncatalytic reduction process

NH3 as reducing agent in selective noncatalytic reduction (SNCR) is widely used for the deNOx of coal-fired boiler flue gas, where fly ash significantly influences the conversion of residual NH3 that does not participate in deNOx. However, few studies have been conducted on the exact nature of this influence. The adsorption and reaction of NH3, NO, and O2 on the fly ash at 50–850 °C were investigated in this study. At 50–350 °C, NH3, NO, and O2 co-adsorbed on the coal ash surface, and the presence of NO and O2 reduced the physical adsorption of NH3 on the ash and promoted its chemical adsorption on the ash. At 450–850 °C, coal ash catalyzed NO reduction by NH3 and NH3 oxidation by O2. In the presence of O2, the oxidation reaction became dominant and the reduction reaction was inhibited. The mechanism of adsorption and reaction of coal ash showed that NH3 was adsorbed on the Brönsted and Lewis sites on coal ash and NH3 at the Lewis site could be dissociated into *NH2 and *NH. The NO ad-species in coal ash were mainly nitrate and nitrite. *NH2 reacted with NO to form NH2NO, which desorbed as N2 at 450–850 °C. The main oxidation intermediates for NH3 ad-species were monodentate nitrate and bridged nitrate, which desorbed as NO at 450–850 °C. The results provide a theoretical basis for adjusting the migration and conversion of residual NH3 and reducing ammonia slip from power plants.