Preheater Research Articles

Experimental Study on a Flue Gas Waste Heat Cascade Recovery System under Variable Working Conditions

Recovering flue gas waste heat is beneficial to improving the unit efficiency in power plants. To obtain the change rules of performance parameters of a flue gas waste heat cascade recovery system (FWCRS) under variable working conditions, an experiment bench was designed and built. The variation laws of the inlet temperature and exhaust flue gas temperature of a low temperature economizer (LTE), the inlet and outlet air temperature of an air preheater (AP), the heat exchange quantities of the AP, LTE, and front-located air heater and an additional economizer (AE), as well as the waste heat recovery efficiency, the system exergy efficiency, and the energy grade replacement coefficient were obtained as the flue gas flow, flue gas temperature, bypass flue gas ratio, air temperature, and circulating water flow in AE changed. Using an orthogonal test, the flue gas temperature, bypass flue gas ratio and air temperature were proved to be the significant factors affecting the performance parameters of FWCRS, and the bypass flue gas ratio was suggested as an adjusting parameter of FWCRS under variable working conditions.

Parameters influencing wet biofuel drying during combustion in grate furnaces

Mainly grate-fired furnaces are used for heat production, as these systems are designed for high thermal efficiency with low emission levels of gaseous pollutants when firing good quality biomass with 30–45% moisture content. However, high demand for biomass during the winter makes it necessary to necessitates use wet biofuel of lower quality with varying moisture content that can reach up to 60% wt. causing the burning instability and incomplete combustion. These negative effects could be avoided by optimizing the furnace control to intensify biomass drying on the grates, but the parameters affecting wet biofuel drying must be known. In order to expand the knowledge of the wet biofuel drying process and establish the parameters that influence the drying process most significantly, a special rig based on characteristics of a 6 MW grate furnace was produced and drying experiments simulating the primary air flow in the furnace, the recirculation of the flue gases and the primary air flow together with exposure to thermal radiation were performed. The results revealed that the radiation from surfaces has the biggest impact on biomass drying when preheated air of the temperature of 200 °C is supplied and the moisture content of the biomass is reduced to 0.66 of its initial value. It was also determined that the drying intensity depends on the mixing period and the drying intensity can be increased by up to 15% by additional mixing. Influence of the drying agent temperature depending on the particle size was established as well.

Energetic analysis of reheating furnaces in the combustion of coke oven gas, Linz-Donawitz gas and blast furnace gas in the steel industry

The reheating furnace of the steel industry was evaluated in the present study, which uses the gas mixture from coke oven (COG), steelmaking process “Linz-Donawitz” (LDG) and blast furnace (BFG); with the production of steel laminates being its main activity. Two methods were developed in this work to deal with energy consumption. The first dealt with improved estimation of heat losses in the furnace, and the second dealt with recovery of heat and its use in load preheating and combustion air preheating. These evaluations were intended to determine the best selection of material for insulation of the furnace, in order to increase heat transfer, to obtain an economy in fuel consumption, and to improve technical energy indicators of production and heat generation, as well as to improve the efficiency of the furnace and the combustion process. When developing the present study in the reheating furnace it was evidenced an economy in the fuel consumption of the COG/LDG mixture of 6606 m3/h and 4627 m3/h for the load preheating and the air preheating, respectively. In addition, efficiency of the furnace was increased by 23.3% and 15.2%, with the technical energy indicators improved by 18.9% and 13.2% in each case. For the COG/BFG mixture, the results obtained were similar.

Failure analysis on cracking of backing plate of lifting lug for air preheater

The breakage of the lug pads and the barrel welds on the air preheater is a common problem. This paper analyzes the fracture failure during the operation of the air preheater. Through the investigation of the working environment of the air preheater, the fracture morphology detection and the microstructure observation, the finite element method is used to predict the welding residual stress and thermo-mechanical stress at the lug pad and the barrel weld. The results show that the microstructure degration at high temperature and high thermomechanical stress synergistic effect are the main factors leading to the fracture with mixed mode of ductile fracture with dimples and brittle fracture with fluvial cleavage pattern. Last, some suggestions were put forward to avoid fracture during hoisting.

Design and Operational Analysis on Natural Gas-fired Cupola

Due to environmental regulations and social obligation towards society, more and more attention has been paid to the natural gas-fired for its excellent performance of environmental protection, energy saving and green economy. The present paper is devoted to the design and operational analysis aspects of natural gas-fired cupola. The basic structure of natural gas-fired cupola, including combustion section, melting section, preheating section and cupola well, etc has been discussed. The key technologies of burners, water-cooled grates, lining refractory, refractory balls, air preheater and cupola well are analyzed, and the basic parameters are determined. The melting process is briefly introduced, and the thermal balance of the whole furnace is analyzed. Application of the test in the case shows that natural gas-fired cupola has obvious advantages and high practical value.

Application and performance evaluation of desulfurization wastewater spray drying technology

In order to realize zero discharge of desulfurization wastewater, spray drying technology of desulfurization wastewater was used in 2x330MW unit of a power plant. Its principle was to use a rotary atomizer for atomization,and a part of hot flue gas was drawn from the SCR denitrification reactor and air preheater into the drying tower, the heat was used to evaporate the desulfurization wastewater in a spray drying tower. The salt in the waste water was mixed with the dust, which was collected and removed by the electric dust remover. Then the water vapor was mixed with the flue gas and finally enters the desulfurization tower.The field test was carried out under the condition that the unit load was 100% and the amount of desulfurization wastewater treated was 5.1m3/h.The results showed that the hot smoke gas volume of drying tower was about 64896m3/h, The smoke temperature at the inlet and outlet of the drying tower were 335℃ and 205℃ respectively,the moisture content of drying products was only 0.05%. The content of HCl in the flue gas at the inlet and outlet of the drying tower were 55mg/L and 195mg/L respectively, the mass fractions of Cl removal and Cl volatilization in desulfurization wastewater were 87.7% and 12.3% respectively. The increase of Cl content in the dried products had little effect on the utilization of fly ash.

Numerical investigation and performance enhancement of 210 MW boiler by utilization of waste heat in flue gas

The developing trend of increase in the price of fossil fuels forced the industries to find alternative energy sources and minimize heat loss. The utilization of waste heat in industries plays a pivot role to reduce the fuel consumption and emission of greenhouse gases. Overall it leads to a reduction in the cost of production. It is observed from the coal fired power plants, that the temperature of flue gas at the exit of the air preheater, which is the final regenerative device and, a proportionate amount of heat is carried away by way of the flue gases to the atmosphere. A substantial amount of fuel may be saved by way of utilizing the thermal energy from flue gas. Due to this saving, the performance of the boiler can also be increased considerably. A heat exchanger is used to extract the heat from flue gas to working fluid. The waste heat from the flue gas can be utilized to heat the feed water coming out from the condensate extraction pump. Feedwater gets heated once it gets into the heat exchanger. The heat exchanger is placed after the air preheater and it is analyzed in ANSYS 14.5 software. The effectiveness and efficiency of the heat exchanger is estimated to be 0.61 and 68.32% respectively. This heat exchanger could be used to save 6527.77$ in coal consumption by annually. This is accomplished through without traumatic the original machine in the power plant.

Curtain Wall with Solar Preheating of Ventilation Air. Full Scale Experimental Assessment

Heating load in Commercial buildings is highly related with ventilation systems, while at the same time local discomfort in the vicinity of glass walls occurs due to overheating. In this paper, a novel double envelope curtain wall is presented, which extracts heat from the façade by means of a ventilated cavity which is then incorporated to the ventilation air intake. A substantial reduction of heating loads is achieved. Whenever solar gains are not sought, a bypass element allows the natural ventilation of this air cavity, acting as a ventilated façade. An integrated control system with embedded electronics and actuators allows for a smart control of the system. The system is designed for integration with existing rooftop ventilation systems. Design considerations are discussed, and the outcomes of a full-scale experiment conducted in Bilbao (Spain) along 2019 presented.

Experimental study on combustion of CH4/NH3 fuel blends in an industrial furnace operated in flameless conditions

This paper presents the results of an experimental study on the combustion process of methane mixed with NH3 in flameless mode. At a time of striving for CO2-free power, NH3 became a potential energy storage carrier fuel from renewable sources. Flameless combustion features low emissions and is a very efficient technology used in the power sector, as well as steel production, ceramics, etc. Industrial furnaces were tested in the context of pure methane combustion with an addition of NH3, up to 5%. Flameless combustion conditions were achieved with a regenerative gas burner system (high regenerative system). The burner consists of four ceramic regenerators allowing for continuous preheating of air, even up to 50 K lower than the temperature of the combustion chamber wall. Constant power of the introduced fuel was kept at 150 kW and the fuel-air equivalence ratio ranged from 0.75 to 0.95. The results have shown a growth of molar fraction of NO in flue gases when NH3 content in the fuel rose. The increase is more significant for the tests with a higher amount of oxygen in the combustion chamber (a lower fuel-air equivalence ratio). An addition of 5% of NH3 into the fuel caused an emission of NO at the levels of 113 ppmv and 462 ppmv (calculated to O2 = 0%), respectively for low and high fuel-air equivalence ratios.

Effect of Pre-Heated Air on Spark Ignition Engine Fuelled with Petrol-Ethanol Blends

Bio-fuels have been made vital developments from past decades, in which bio-petrol plays a major role in SI engines. Developments in petrol-ethanol blends have been made to improve the efficiency of SI engine. Air preheated is supported widely in preheating of intake air. To improve efficiency and to reduce emission, air preheated is used in many systems. SI engines are used in automobiles, motor cycles, aircrafts, motorboats and portable small engine. In this work, investigations have been done in the SI engine which intakes preheated air-fuel mixture and various blends of ethanol petrol fuel is used as working fuel. Emission tests are done by exhaust gas analyzer to compare the emissions of different fuels.

A shallow cross-flow fluidized-bed solar reactor for continuous calcination processes

A laboratory-scale solar reactor prototype dedicated to calcination processes of non-metallic mineral particles is tested and characterized. The prototype consists of an indirect heating shallow cross-flow fluidized-bed reactor-receiver. It is composed of 4 compartments in series in which the particles are thermally treated with solar power in order to drive the endothermic calcination reaction. The particles are fluidized in the reactor with preheated air and are heated up to 800 °C through the front wall of the reactor receiving the concentrated solar flux (about 200 kW/m2). The tests are carried out at the 1-MW Odeillo’s solar furnace (France). The thermal decomposition of a continuous stream of 9.4 kg/h of dolomite (CaMg(CO3)2) is investigated in this paper. The half decomposition of dolomite (CaMg(CO3)2 → CaCO3 + MgO + CO2) is performed with a degree of conversion of 100%. The complete decomposition of dolomite (CaMg(CO3)2 → CaO + MgO + 2CO2) is not reached because, with respect to the CO2 partial pressure in the reactor, the temperature of particles is not high enough to decompose the calcium carbonate. The calculated thermochemical efficiency (i.e. the energy absorbed by the endothermic calcination reaction compared to the solar energy provided to the system) is 6.6%. This low efficiency is neither surprising nor critical since the reactor design was not optimised with respect to energy efficiency but designed to the control of particle flow and front wall solar flux distribution. A numerical model considering the 4 compartments of the reactor as 4 ideal continuous stirred tank reactors in series is developed. The model accounts for the mass and the energy balances, as well as the reaction kinetics of the half decomposition of dolomite. The model gives consistent results compared to the experimental data. These results are a proof of concept of continuous calcination reaction using concentrated solar energy in a cross-flow fluidized-bed reactor.

On Preheating of the Outdoor Ventilation Air

The growing popularity of buildings with integrated sub-systems requires a review of methods to optimize the preheating of ventilation air. An integrated system permits using geothermal heat storage parallel to the direct outdoor air intake with additional treatment in the mechanical room as a part of building an automatic control system. The earth–air heat exchanger (EAHX) has many advantages but also has many unanswered questions. Some of the drawbacks are: A possible entry of radon gas, high humidity in the shoulder seasons, and the need for two different air intake sources with a choice that depends on the actual weather conditions. In winter the EAHX may be used continuously to ensure thermal comfort, while in other seasons its operation must be automatically controlled. To generate missing information about EAHX technology we examined two nearly identical EAHX systems, one placed in the ground next to a building and the other under the basement slab. In another project, we reinforced the ground storage action by having a heat exchanger placed on the return pipes of the hydronic heating system. The information provided in this paper shows advantages of merging both these approaches, while the EAHX could be placed under the house or near the basement foundation that is using an exterior basement insulation.

Thermodynamics Analysis of Solar-Rice Husk Hybrid Power Plant

The main objective of this study is to make thermodynamics analysis of different components of solar rice husk hybrid power plant with its modification of structure by implementing a Rice Husk Dryer between the Condensate Pre-heater and Air Pre Heater in order to feed dry rice husk to furnace and performance evaluation of power plant with respect to reduction of moisture content of rice husk using MATLAB, R2016a. The flue gas is passed to the Rice Husk Dryer, where the heat of flue gas is used to dry the rice husk before feeding to the furnace. Solar energy is limited to a 50% share in the daytime. In this research solar parabolic collector and Rice, husk feed is arranged in a parallel to produce steam. Feeding with dry rice husk in the furnace was found to reduce the heat loss due to heating moisture present in rice husk up to furnace temperature and also heat loss due to excess air supplied to the furnace for evaporating and superheating the moisture present in the rice husk. The increase in furnace efficiency, fuel efficiency, thermal efficiency and plant efficiency, reduction in specific rice husk consumption, reduction in excess air supply and decrease in rice husk consumption, etc. with respect to reduction in the moisture content of rice husk for the power plant are evaluated. The result showed that with the reduction of moisture from 10% to 90%, the power plant efficiency is to be increased by 6.97% to 64.86% for boiler pressure of 50 bar.

Performance evaluation of a new conceptual combustion air preheating system in a 1000 MW coal-fueled power plant

An innovative design of combustion air preheating for large-scale coal-fueled power plants was proposed. Differing from the conventional air preheating system using a rotary regenerative air preheater, a cascade heating concept is adopted in the new configuration, where the air obtains heat from the feedwater, circulating water and flue gas in several tubular heat exchangers, which significantly diminishes the air leakages and the exergy destruction. The results of a detailed thermodynamic analysis show that, for a typical 1000 MW coal-fueled power plant, the net thermal efficiency increment can reach 0.49% points with a net heat rate reduction of 86.77 kJ/kWh, if the novel air preheating design is adopted instead of the conventional one. This is because the exergy efficiency of the air preheating process is promoted from 77.88% to 91.77% owing to the proposal, and the total exergy efficiency of the power plant rises by 0.48% points. The economic performance of the new design was examined as well, indicating that the dynamic payback period is only 5.30 years when the proposed air preheating system is employed to replace the conventional one. This work may be beneficial for enhancing the air preheating system and advancing coal-fired power production.

Physical Cavity of a Double Skin Facade as a Source of Pre-Heated Air in the Winter Season for the Heat Recovery Unit of a Facade

Abstract This paper deals with the use of pre-heated air in the winter season for the heat recovery unit of a facade. Heated air is transformed from solar radiation in the cavity of a double skin facade with a narrow space cavity. The height of a section is equal to one storey. With the help of mathematical modelling simulations (CFD tools), increases in temperature are quantified in the cavity of the double skin facade. The increase in temperature depends on the air flow and the intensity of the solar radiation. In conclusion, it summarizes the positive effect on heat recovery from the air exhaust to preheat a fresh supply of air from the double skin façade’s cavity. This approach can increase the efficiency of any heat recovery and reduce heat loss from the ventilation.

Optimasi siklus termodinamika integrasi boiler AQC dan PH pada desain WHRPG di industri semen

The cement industry is a chemical industry that requires large amounts of energy and releases CO2 emissions, one of which is produced from limestone calcination. Electricity consumption index for 2017 at PT Holcim Indonesia Tbk. Cilacap Plant averaged 92.20 kWh / ton cement and 3,352MJ / ton clinker in thermal form. This shows that the use of thermal energy is very dominant in the production process. The opportunity to reduce the index of electricity consumption is a very appropriate step in order to reduce greenhouse gas (GHG) emissions and production costs, thereby increasing its competitiveness. Installation of WHRPG system in the preheater (PH) process output unit and the water quenching cooler (AQC) output to utilize exhaust heat that can produce pressurized steam and when combined with the steam turbine starter drive and electric generator coupled, the system is able to generate electricity to supply the needs electrical energy industry. From the data of potential exhaust gases in PH and AQC and the design determination of the choice of operating conditions of the selected three-level steam turbine pressure, the optimization results are obtained by applying a graded nonlinear GRG model, the thermal efficiency of the WHRPG water system is optimal at 24.38% with work output the optimum thermal value is 6,420.29 kW and the estimated gross electric power yield is 6.089,51kW. The optimal conditions achieved are indicated by the pinch point value on the AQC boiler that occurs in the economizer at 10K while the PH boiler occurs at the superheater of 10K according to the specified pinch minimum constraints. If the estimated power of the balance of plant and auxiliaries in the WHRPG system is 12% and the cement production capacity is 7,800 tons / day assuming a WHRPG capacity factor of 73%, then the magnitude of the reduction in electrical energy intensity is at least 12.04 kWh / ton cement.
 Keyword : Preheater, Air Quenching Cooler, WHRPG, HRSG, Cement, GRG nonlinear, Optimamization, Kawasaki

Neuro-Fuzzy Logic Based Robust Detection and Isolation of Economizer and Air Pre-Heater Faults in Steam Boiler

The technique of Fault Detection and Isolation (FDI) of Economizer and Air-preheater of Boiler using Neuro-fuzzy system is presented in this paper. FDI using model based approach and intelligent methods are the current trend applied in space industries, process industries and power plants. Intelligent methods like Fuzzy, Neural network and Neuro-fuzzy methods are simpler for modeling and faster for detection and isolation of faults. Here the water wall type steam boiler which is used for producing steam in fertilizer industry is studied. The proposed scheme is detecting and isolating the faults and failures happens in the economizer and air preheater of boiler. The common faults are corrosion, erosion, cracking of boiler tubes at welding points, tube rupturing, scale formation in the tubes, external ash deposits etc. The inherent non-linearity of boiler makes Neuro-fuzzy logic method suitable for FDI for all possible faults. The detection of faults is carried out by computing residuals, which are the differences between real process output and estimated output by neuro-fuzzy logic model. These estimated outputs were obtained from the neuro-fuzzy logic model which is trained using real time data by Adaptive Neuro-fuzzy Inference Systems (ANFIS). The real time data of economizer and air-preheater of boiler is collected and used for residual generation. The residuals will be formed for two outputs which are playing important role. If the residual exceeds threshold value indicates various faults in the boiler components and makes the proposed FDI scheme robust against process and measurement noises, process modeling error, disturbances and all uncertainties etc. The threshold band is calculated using model error model method. To isolate the faults, the residuals are normalized and its magnitudes are compared with present fault severity limits. More the range of severity more will be the magnitude of faults in the boiler. FDI by neuro-fuzzy method is more advantages as it combines the advantage of artificial neural network and fuzzy logic methods. The neural networks are more adaptable and have more learning ability. Fuzzy systems are dealing with human reasoning and decision making. As a result the designed FDI scheme is more sensitive to faults and less sensitive to uncertainties and disturbances etc. makes the scheme robust. The required data and fault knowledge for the research work is collected from BHEL make 55 tons per hour capacity, water tube type boiler available in Madras fertilizer Limited (MFL), Chennai.

Achievement in ultra-low-load combustion stability for an anthracite- and down-fired boiler after applying novel swirl burners: From laboratory experiments to industrial applications

Deep peak shaving requires extremely high requirements for low-load combustion stability of boilers. In this study, a novel swirl burner (NSB) with an eccentric secondary air arrangement was proposed, and the validity and the progressiveness of the NSB in achieving ultra-low-load combustion stability for down-fired boilers (DFBs) were confirmed from laboratory experiments to industrial applications. Firstly, the cold-modelling experiments of gas/particle (GP) two-phase flow characteristics involving two combustion systems (i.e., the DFB with traditional swirl burners (TSBs) and the DFB with NSBs) were performed at an ultra-low load of 90 MWe. Compared with the original boiler with TSBs, the maximum horizontal recirculation velocity and the area of recirculation zone below arches significantly increase for the improved DFB with NSBs. The particle number concentration near furnace center for the improved DFB with NSBs is much higher than that for the original DFB with TSBs. The above two aspects will effectively guarantee timely ignition of anthracite. The downward depth of GP flows and the space utilization ratio of the lower furnace increase, which will be beneficial to promoting volume heat load and heat flux density in primary combustion zone. In addition, full-scale industrial-sized measurements aiming at a 300-MWe DFB improved by NSBs were carried out at ultra-low loads of 100 and 90 MWe. For the original DFB after improved by NSBs, the minimum load for stable combustion without oil support is reduced from 150 to 90 MWe, and the ultra-low-load combustion stability is achieved. For the improved DFB with NSBs, pulverized coal ignition distances for operating burners are about 2 and 2.6 m, respectively, and the signal strength of flame detectors for all operating burners is above 95% at 100 and 90 MWe. The flame fullness and combustion stability are good at the initial combustion stage. At ultra-low loads, furnace negative pressure, superheat steam pressure and oxygen concentration at furnace outlet fluctuate slightly. The temperature at air preheater inlet meets the needs of normal operation of denitrification system, and there is no problem of low temperature corrosion on the surface at flue gas side of air preheater. The unburned carbon in fly ash is about 4%. The maximum concentrations of NOx emission at furnace outlet are 714 and 687 mg/m3 (O2 = 6%) at 100 and 90 MWe, respectively, and ultra-low emission of NOx after denitrification system is achieved.

Experimental study on the ash deposit thermal conductivity for ammonium bisulfate and fly ash blend with an in situ measurement technology

Ammonium bisulfate (ABS) deposition is a severe problem in economizers and air preheaters, since it will result in the blockage of preheater, decreasing the efficiency and the corrosion of downstream devices. The blend deposition characteristics of ABS and fly ash blend, including thickness, effective thermal conductivity and heat flux through the probe surface, are investigated with an in situ measurement technology. The low flue gas temperature and high blending rate could promote the growth of blend deposit. The stable thicknesses of the blend deposits at different flue gas temperatures are 10.20 mm, 7.64 mm and 5.21 mm for different furnace temperatures (Case A, B and C, respectively). The stable thicknesses of the blend deposits with different blending rates are 10.20 mm, 5.52 mm and 3.36 mm for different blending rates (Case A, D and E, respectively). The effective thermal conductivities of blend deposits at the stable stage are 0.413, 0.397, 0.387, 0.357 and 0.28 W/m/K for Case A, B, C, D and E, respectively. In order to clarify the mechanism of the blend deposition, XRD and SEM-EDX are applied to analyze the blend deposits. The results indicate that the ABS content in blend deposit decreases with the increasing flue gas temperature and increases with the increasing blending rate. Meanwhile, the blend deposit with high ABS content has a more compact microstructure, a higher strength and a greater effective thermal conductivity. The results contribute to an insight into the ABS deposition characteristics in economizers and air preheaters.

Study on the formation process of low‐temperature ash deposition induced by ammonium bisulfate in pulverized coal‐fired boiler

AbstractIn order to explore the mechanism of low‐temperature ash deposition induced by ammonium bisulfate (ABS), ash deposits, and a corroded heat transfer plate in the rotary air preheater (RAPH) of a 1,000‐MW pulverized coal‐fired power plant in China were analyzed by X‐ray fluorescence, ion chromatography, X‐ray diffraction, and scanning electron microscope equipped with energy dispersive X‐ray spectroscopy. The element composition, main compounds, and ammonium ion in the samples were analyzed. The thermal gravimetric analysis of ash samples was conducted to infer the type of ammonium salt ultimately existing in the ash. The prediction of the ABS deposition range coincides well with both the area of serious ash deposition and the area of NH4+ distribution obtained by ion chromatography. The cause for corrosion and plugging in the RAPH was proposed by analyzing the reactions or mineral transformations involved in the ash deposits. The results indicate that ABS can form in a large height range in the RAPH. The ammonium induces the sulfur trioxide to deposit on and react with the metal plate or the ash particles to form sulfates, which act as the bridging agent, finally leading to serious plugging problems in the RAPH.