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Conventional natural gas-fired boiler exhaust flue gas contained large amount of waste heat and water vapor direct to the atmosphere at high temperature which results in relatively low thermal efficiency. In traditional ways only a part of sensible heat are recovered. The latent heat, contained in the water vapor, which is the majority of the waste heat in the flue gas, cannot be recovered. Using a heat pump system with a boiler, the temperature of flue gas of the boiler can be drooped to dew point and the waste heat in the flue gas and condensation heat can be recovered deeply. In this paper, a new type of system, absorption heat pump vs. boiler, is proposed in which the waste and vapor in flue gas can be recovered efficiently. In this system, not only the evaporator is used to absorb the waste heat from flue gas, but also the generator is used to get the heat from the flue gas at high temperature. At the same time, a heat exchanger is used to transfer the heat from the flue gas to the backwater. A collector is installed on the evaporator to collect the condensed water from flue gas which will be used to a feed-water for the boiler room after they are purified. The performance of system is evaluated basing on a practical project, the installed capacity of which is 31.5MW. Results show that with the system, 13793.84MJ of heat is recovered per hour, in a whole heating season, 1.14 million cubic meter of natural gas will be saved. The efficiency of boiler rises about 11.8%. The recycled condensed water is 1177.344m3. 227 tons of CO2 can be cut into atmosphere per year.

In order to develop suitable low-low temperature flue gas system for China and determine its operation parameters, the adsorption characteristics of ash particles for sulfuric acid mist need to be investigated, as well as the adhesion characteristics of ash particles after the adsorption. In this paper, experiments were conducted on a laboratory-scale fixed bed adsorption reaction system. The adsorption characteristic curves of different particle sizes and adsorption temperature were obtained. The results show that adsorption temperature has a larger influence on the adsorption process compared with particle size. And there exists an adsorption limit in the adsorption process. In addition, the ultimate D/S (Dp/Sp) of ash particle is defined, which means the ratio of ash particle weight (mg) to adsorbed H2SO4 weight (mg) when ash particle reaches the adsorption limit. It is an inherent attribute of ash particle, only influenced by the particle constituents and sizes, representing the ultimate adsorption capacity of ash particle for sulfuric acid. The experiment results show that the chemical constituents of ash are the main determinate factors of adsorption limit and the Dp/Sp. And the Dp/Sp could be used cooperatively with D/S when people design the parameters of low-low temperature flue gas system for different types of coal. Furthermore, there was a significant agglomeration phenomenon between ash particles after the adsorption reaction, and it can increase the average size of particles which is conducive to the removal of PM.

The ash-related issues due to the high-alkali characteristic are still unresolved during utilization of biomass and Zhundong coal. Here, the correlations of several chemical properties of high-alkali solid fuels were investigated. The distributions of ash compositions in various biomass exhibit obvious diversity, while the distribution of K 2 O content within wheat and corn straws are the most scattered. The ash content in biomass shows a decrease tendency with the increase of carbon content. Zhundong coals generally have medium but close ash fusion points despite of quite different ash compositions sometimes.

The utilization of high-alkali coals in Zhundong coalfield with oxy-fuel combustion technology has a great potential, however, the ash fusion properties of high-alkali coals are still unclear. Here, we studied the influence of oxy-fuel atmosphere on the microscopic properties of high-sodium ash. The change from air to oxy-fuel condition has a negligible influence on ash fusion temperatures, but exhibits certain impact on physical-chemical properties of high-alkali ash. Oxygen content presents a primary effect on the microscopic morphology of ash at softening temperature.

Low-low temperature flue gas system which also called MHI high efficiency system developed by Mitsubishi Corporation has gained comprehensive attention in Japan, European countries and American. However, the applications of this system in China are facing several sever problems about corrosion and ash fouling. This paper focuses on the adsorption characteristics of sulfuric acid mist on fly ash during the flue gas cooling process in the exchanger before the electrostatic precipitator. The experimental results indicate that there is an optimum adsorption temperature for the adsorption of sulfuric acid mist, and this temperature is about 30 ℃ lower than the acid dew point. The process of adsorption is mainly dominated by chemical reactions rather than physical reactions, and the alkali metals (Na, K) and alkaline earth metals (Mg, Ca) are the main factors which influence the chemical reaction rate, especially the Na element. Besides, with the D/S increasing, the adsorption efficiency increases and it is independent of the adsorption temperature. Ash particle size also has large influence on the adsorption efficiency, the smaller the particle size is, the larger the adsorption efficiency is. And when the flue gas speed rose, gas residence time correspondingly reduced and the adsorption efficiency dropped. However, since gas residence time is short in engineering applications, the influence of gas residence time is quite moderate. Furthermore, the adsorption of the sulfuric acid mist will cause a significant agglomeration between ash particles, and it has great significance to the removal of PM.

To investigate the release and transformation of fuel K during combustion of biomass, wheat straw and corn stalk are burnt in a fixed-bed reactor system during 400−1000 °C, and weight measurement, elemental composition analysis, and chemical fractionation analysis are performed. The influences of fuel type, combustion temperature, and water washing pretreatment are discussed. The results show that wheat straw has a higher K release ratio than corn stalk, especially when combustion temperature is above 500 °C. For both biomass fuels, the released K is far less than the water-soluble K. For wheat straw, some of the other occurrence modes of K turn into the insoluble K gradually. For corn stalk, the water-soluble and ion-exchangeable K turn into HCl-soluble and insoluble K. Water washing removes all the water-soluble K of corn stalk and reduces the K release from 3.26 to 0.27 mg g -1 at 1000 °C.

H-type finned tube is rarely used in waste heat recovery power generation stations, though it has an efficient heat transfer performance in large thermal power stations (WHRPGs, hereafter). To date, understanding of heat performance of H-type finned tube in WHRPGs is still lacked. The heat transfer characteristics of H-type finned tube in gas with high content of ash in WHRPGs was investigated in practical cement plant in present work. The actual ash deposition pattern was observed meanwhile. The characteristics of heat transfer process including heat transfer coefficient, heat effective coefficient, and flue resistance at gas velocity between 4.5 - 6.5 m·s –1 are obtained. Experimental results show that the heat transfer coefficient increases with gas velocity linearly, the heat effective coefficient nearly keep stable on the other hand, and serious ash-block problem occurs in flow area in the heat exchanger at the gas velocity of 4.5 - 6.5 m·s –1 . The max heat transfer coefficient remain below 10 w·m –2 ·k –1 , implying heat performance of H-type finned tube in WHRPGs is possibly inefficient.

Raw cement ash deposition in SP boilers gives rise to serious operation problems. In the present, mechanism of raw cement ash deposition is still unclear because the ash components, gas atmosphere and gas temperature are quite different from existing studies. The characteristics of cohesiveness of raw cement ash in moderate temperature were investigated in a lab-scale electric furnace. Three typical raw cement ashes were selected as samples, three base plates, including rough steel plate, smooth steel plate, organic glass plate were studied. Ball-impacting method was adopted to evaluate the cohesiveness of ash. Experimental results show that, the ash cohesiveness is mainly dependent on the components of ash, and the material property of base plate, while it exhibits little relationship with the roughness of the plate surface. Low-melting substances appear during ash deposition on steel plate. The results reveal that ferrum possibly has catalytic to some low-melting substances forming.

The influences of operating conditions, such as excess air ratio and SOFA arrangement, on temperature distributions, species distributions, NOx emissions and burnout of a tangentially-fired utility boiler using bituminous and blended coal were investigated by numerical approach in the present study. The simulation results show that the fuel type exhibits certain effect on the temperature distributions and the NOx emissions. Moreover, higher excess air ratio could restrain the CO formation but promote NOx emission. The temperature and the species distributions are highly related to the SOFA arrangement. In addition, SOFA technology is still an effective approach to control the NOx emissions during blended coal combustion, while the disadvantageous effect on char burnout should be considered.

Oxy-fuel combustion is recognized as one of the most promising CO2 capture technologies. Under oxy-fuel combustion, the concentrations of CO2 and H2O are much higher, result in different temperature profiles and heat transfer properties. In this study, a modified computational fluid dynamics (CFD) model-was developed for a 600 MW tangentially-fired boiler. Different oxygen volume fractions and two flue gas recycle modes (dry recycle and wet recycle) were numerically investigated, focusing on the properties of combustion and heat transfer. The results indicate the peak temperature in the burner zone decreases in oxy-fuel combustion, because of the high heat capacity and chemical reactivity of CO2. Compared with air-fired combustion, similar total heat transfer rate in furnace can be achieved at 27.0% and 28.3% of oxygen volume fraction for wet and dry recycle. These findings indicate retrofitting an existing boiler with oxy-fuel combustion technology is entirely feasible.

Ash deposition is particularly serious during Zhundong coal combustion/gasification due to its high alkali metal content, which causes great troubles and limits its utilization. This paper focuses on the ash deposition characteristics and migration disciplinarian of akali metal during Zhundong coal gasification varing with different conditions, such as ash deposition temperature, gasification temperature, O 2 /coal, steam/coal, and deposition time. Experimental result indicates that gasification conditions play a significant role on ash deposition. The root cause of severe fouling is the high content of Na in Zhundong coal, most of which is water-soluble. Besides, the contents of Na, Fe, S, Cl in ash are obviously changed with flue gas temperature increasing, indicating these elements have great influence on ash deposition, and the migration of Na, Fe and Cl presents similar variation during deposition. In addition, Na deposits mainly above 873 K, and Fe gains enrichment in ash at various temperatures. With the increase of gasification temperature, the content of Na in the ash is increased, which could exacerbate ash deposition. Both O 2 /coal and steam/coal have a certain influence on migration of elements, and the increases of O 2 /coal and steam/coal can relieve the ash fouling phenomena. Deposited ash on heating surface will react with Na in flue gas at high temperature, leading to the increase of content of Na in the ash with deposition time increasing.