Gas-fired Boiler Research Articles

An Experimental Study on the Combustion Characteristics of a Methane Diffusion Flame within a Confined Space under Sub-Atmospheric Pressure

Gas-fired boilers, gas stoves, and wall-mounted gas boilers are the main consumers of gas fuel, but they generally encounter problems when operating at high altitudes, such as reduced thermal efficiency and increased pollutant emissions. Previous studies on gas combustion characteristics under sub-atmospheric pressure were mostly carried out in a large space, which is quite different from chamber combustion equipment. Therefore, it is insufficient to guide the design and operation optimization of plateau gas equipment. In this paper, experimentations were carried out to explore the characteristics of a methane diffusion flame under sub-atmospheric pressures. The mass flow rates of methane and air remain consistent under different pressure conditions. The centerline temperature (Tc) distribution, flame appearance, smoke point, CO emission, and NOx emission under different pressures (ranging from 61.66 to 97.75 kPa) were examined under both fuel rich and lean conditions. The results show that Tc at the rear and front of furnace variation with pressure is opposite under fuel-lean and -rich combustion. The Tc at the front of furnace decreases with decreasing pressure, whereas Tc at the rear of furnace increases with decreasing pressure. With decreasing pressure, flame length decreases under lean combustion, but increases under rich combustion. The smoke point fuel flow rate, flame length, and residence time increases with decreasing pressure, following the law of negative exponent. The CO emission decreases with decreasing pressure, which indicates that the reduced pressure makes methane combustion more complete. For NO emission, the reduced pressure results in an opposite tendency under fuel-lean and -rich combustion. With decreasing pressure, the NO emission decreases under fuel-lean combustion but increases under fuel-rich combustion.

Analysis of the Causes of the Emergency Shutdown of Natural Gas-Fired Water Peak Boilers at the Large Municipal Combined Heat and Power Plant

The paper presents a cause-and-effect analysis of the failure of a 130 MWt gas-fired water boiler. The fault was a rupture of the helically finned tubes in the first rows of the second-stage water heater (ECO2). The high frequency of failures forced the boiler user to investigate their causes. The rapid drop in water flow in the ECO2 and the tightly finned pipes suggested that the permissible operating temperature of the steel used was exceeded. The only possible way to assess the working conditions was through a CFD simulation of the operation of the ECO2. Validated with the data acquisition system, the results show that the main reason for the failure was the overheating of the first rows of finned water heater pipes, regardless of the boiler load. The high heat flux value, exceeding 500,000 W/m2, and the increased flue gas temperature in front of the ECO2, almost reaching 900 °C, affected the appearance of the boiling film, limiting the cooling of the tube wall. Heat radiation and eddies behind the tubes significantly impacted the non-uniform temperature distribution, resulting in high pipe wall stress. By analyzing the service life of the first row of pipes based on the Larson–Miller parameter, it was concluded that the pipes would fail after only a few tens of hours.

A physically based air proportioning methodology for optimized combustion in gas-fired boilers considering both heat release and NOx emissions

Ensuring the reliable operation of industrial boilers with high production efficiency and low pollutant emissions remains a significant challenge due to the complex chemical and physical reactions that occur within the boiler system. To address this issue, the present research introduces a novel air proportioning methodology for optimized combustion in gas-fired boilers, incorporating real-world data, numerical-computational technologies, and a normalization method. Initially, an average discrepancy of 11.32% is observed between the airflow recorded by the sensors and the actual airflow in the gas-fired boiler. The optimum oxygen levels in the flue gas are determined by striking a trade-off between heat release and pollutant emissions. At loads of 35%, 55%, 75%, and 95%, the recommended oxygen levels under equal-weighted conditions are 3.62%, 3.75%, 3.82%, and 3.91%, respectively. Furthermore, this research also considers the oxygen levels when there are non-equal weightings between heat release and nitrogen oxide (NOx) emissions. At 55% load, the weighting between heat release and pollutant emissions shifts from 1:1 to 1:2, necessitating an increase in the oxygen concentration from 3.75% to 4.30%. The air proportioning methodology proposed in this study offers an efficient framework for optimizing combustion in gas-fired boilers.

Techno-economic optimization of high-temperature heat pumps for waste heat recovery

Heat Pumps will play a crucial role in decarbonizing the heat supply, however, the progressive phase-out of environmentally impactful fluids and relevant cost of investments are today limiting the spread of power-to-heat technologies, especially for supply temperatures beyond 100 °C. This paper aims to carry out a comprehensive assessment, investigating the optimal design and most relevant features in different market scenarios. Since iso-butane (R600a) has demonstrated an interesting potential for such an application, it was selected for the purpose of this paper. First, the best heat pump sizing and the contribution of each component are discussed in detail from the techno-economic perspective, through optimization of both efficiency and cost of investment highlighting the greatest impact of evaporator. Eventually, a case study is considered to investigate the viability of replacing gas-fired boilers with HPs to supply heat up to 120 °C. Asensitivity analysis is performed highlighting that the large and centralized heat generationunitsworking almost continuously are generally more attractive. Moreover, this work establishes that when performing a sizing procedure or a sensitivity analysis, it is essential to account for the dependency of retail prices to the yearly energy consumption. The national trends of non-household retail prices are here provided for different countries. A market indicator is here defined, summarizing the market competitiveness of heat pumps vs boilers, combining the gas, and electricity cost, weighted on COP and boiler efficiency, in one single term. This indicator remained stable over the period 2017–2021, characterized by volatile energy market conditions, demonstrating the robustness of the economic conclusions of this paper. Sweden presents the best profitability (up to a net present value of 2.25 M€ for each MW of installed thermal capacity), France and Poland shows intermediate results (ca. 0.6 M€/MW), while in Italy and Germany, the worst markets, the minimum Heat Pump sizes to reach positive profits (ca 0.1 M€/MW) are respectively 1.5 MW and 4 MW.

Experimental study on wet gas condensation heat transfer and flow resistance in horizontal intensified tube

The heat transfer and flow resistance characteristics of in-tube vapor condensation with high content non-condensable gas is significant for designing waste heat recovery devices of gas-fired boilers. In this paper, the forced convection condensation of wet gas in the horizontal tube is experimentally investigated with a non-condensable gas mass fraction of 83–95%. The condensation heat transfer coefficient, thermal resistance and pressure drop are compared between bare tube and two intensified tubes, i.e., the corrugated and spiral tube, under various Reynolds number, wall subcooling degree and inlet humidity. The results show that the in-tube condensation heat transfer coefficient increases with increasing Reynolds number and inlet humidity, but decreases with increasing wall subcooling degree. Compared with the bare tube, the heat transfer coefficient and pressure drop increase up to 47.13% and 16.00% respectively for the spiral tube, and 116.04% and 88.48% respectively for the corrugated tube. When combing the heat transfer and flow resistance factors, the maximum comprehensive performance coefficients are 1.71 and 1.44 for corrugated tube and spiral tube respectively. The superiority of corrugated tube in the wet gas condensation is benefit from effective breaking the non-condensable gas film and promoting the vapor diffusion on the interface.

Energy saving and peak load shifting performance of tail water source heat pump integrated with large-scale thermal storage pool space heating system in technology park

In cities, there are thousands of wastewater treatment plants. The treated tail water drained from them is clean relatively, and has a stable flow rate. Extracting heat from it through tail water source heat pumps (TWSHP) for space heating can decrease the building heating energy consumption significantly. Besides, by integrating with thermal energy storage (TES), it can realize the goal of peak load shifting, especially in commercial buildings. However, there is few reports on its experimental investigations or engineering applications till now. To promote the application of TWSHP integrated with TES system, it was designed for the space heating of a technology park in Beijing, and a control method was proposed to decrease the operating cost by using the valley electricity. Then, utilizing its operating parameters in the heating season of 2021–2022, its heating performance was analyzed. Results indicate that the proposed system has good heating performance. The average COPs of TWSHP units and the system in the heating season are 7.08 and 4.41, respectively. Compared with gas-fired boiler, its carbon emission decreased by 62.53%. By using the TES system, the power consumption during valley period of power grid increases by 581.23%, realizing the goal of peak load shifting.

Numerical Calculation of Wet Exhaust Gas Condensation in the Heat Exchanger

Based on the background of waste heat recovery of gas-fired boiler, this paper studied wet exhaust gas condensation heat transfer using numerical methods. The calculated results indicated that with the exhaust gas Re number increases, heat flux, and Nu number gradually increase, while the Eu number decreases simultaneously. Besides, the variation trend of the Nu and Eu number gradually reduced with Re number increases. With inlet exhaust gas temperature increase, the Nu number increases, and the Eu number decreases. Meanwhile, Nu number and Eu number increases with the increase in wall temperature. On this basis, the empirical correlations for calculating Nu and Eu numbers are obtained, and the deviation between the calculated values and the numerical results is within ±8%. The conclusion of this study provides basis for heat exchanger design in wet exhaust gas waste heat recovery.

Decarbonization performances of a transcritical CO2 heat pump for building heating: A case study

An experimental transcritical CO2 heat pump system was implemented in the severely cold region, Harbin (China), and the energy and exergy performances as affected by the expansion valve opening were compared and the environmental and economic performances of CB (Coal-fired Boiler), GB (Gas-fired Boiler), EB (Electric Boiler), and HP (Heat Pump) were analyzed. The results showed that the system COP decreased by around 0.2 when the expansion valve opening was increased from 60% to 80% with the highest system COP of 2.40. The system exergy destruction and exergy efficiency increased from 5.12 and 33% to 5.61 kW and 37% when an increase in the expansion valve opening from 60% to 80%, respectively. The CO2 and pollutants emissions of HP were 52% ∼ 92% lower than CB and EB. The life-cycle cost of HP for a 15-year working period was the lowest (36.57 × 104 CNY) and it was 84%, 77%, and 39% of CB, GB, and EB, respectively. The results revealed that the transcritical CO2 heat pump system has better environmental and economic performances than CB, GB, and EB, its emissions were 52% lower than CB and EB and its life-cycle cost was only 39% of EB.

Flue gas condensation of solid fuel fired heating plant

In the Czech Republic, increasing trend exists in utilization of biomass as a fuel in heating and power plants. This is preferred solution by EU Climate plans, and it is connected with some economic benefits (e.g. green bonuses, guaranteed purchase price), on the other hand the combustion of fossil fuels is penalized (EU ETS – Emission Trading System). There are many types of biomass with different parameters but one of the most discussed are wooden resides because of its quantity. There are big differences between quality parameters, especially in moisture content, which is decreasing the LHV. There are some technologies which can decrease moisture. Dryer technologies could be simple so-lution, but final decreasing of moisture is quite low. More effective is application of flue gas condensation. This technology is well known for gas-fired boilers but nowa-days is still more often build by new solid fuels-fired plants. This deals with design of condensation technology for existing heating plant in Mladá Boleslav. The fuel mixture is based on wood residues (70 %) and pelletized plant biomass (30 %). The calculation was done for three boilers for soild fuels – two same CFBs (steam production 100 t·h-1) and one BFB (steam production 80 t·h-1). Moisture content was calculated for two cases of wooden residues with moisture content 35 and 50 %. System of condensation include three step water scrubber, heat ex-changer, heat pump and humidifier of combustion air. The final designed output of unit for BFB is 12.7 MW (19 MW for each CFBs), but from these the output of heat pump is 5 MW (7.5 MW). The source of heat for heating pumps is steam, which can be used in current heater, so the final net output from condensation is 7.7 MW (11.5 MW). These parameters are only for 50 % of moisture content in wooden residues. The application of these system is not cost-effective for moisture content of fuel around 35 %. It is possible to build this technology for 50 % of fuel moisture content, but technology will not raise the temperature parameters of hot water. There are two differences between Mladá Boleslav heating plant and Finnish Vuosaari power plant in Helsinky, where the similar unit is already built. First of them is moisture content of fuel more than 50 %. Second one is temperature of hot water system 60 °C, however in Mladá Boleslav is at least 80 °C, sometimes it could be more than 110 °C. The decreasing of this temperature is problem because the most of heating systems were designed by current standards with temperature 80 °C. The only possible solution is to build two steps scrubber and the waste heat utilize as preheater of hot water.

Configuration method for combined heat and power plants with flexible electricity regulation

A net-zero emissions target has been set as the long-term climate goals by many countries and regions. Efficient utilization of renewable energy is an essential way to solve energy and environmental problems. China needs to change its fossil-based energy mix and achieve a deep low-carbon transition in the energy sector. The future development of thermal power plants is focused on improving the power peak-shaving capacity while ensuring a heating supply with economical and feasible methods. This study presents a reasonable evaluation model to analyze different cogeneration plant power peak shaving modes. It proposes an optimal configuration method for combined heat and power generation plant power peak shaving systems by combining their characteristics and applicability. The basic principle of this method is that the most profitable mode for each power peak-shaving depth must be selected to achieve the best overall economic benefit of the system. The absorption heat pump waste heat recovery method, the electric heat pump waste heat recovery method and the electric boiler method are suitable for bearing the base load, waist load and peak load of the power peak shaving, respectively. The analysis results of influence economic factors show that as the heating price of the alternative heat source increases, the electric heat pump waste heat recovery method assumes a larger capacity for power peak shaving. When the heating price of alternative heat sources is 30 yuan/GJ (about the heating cost of a coal-fired boiler) and 100 yuan/GJ (about the heating cost of a gas-fired boiler), the electric heat pump waste heat recovery method should bear the depth peak-shaving demand with the duration higher than 360 h and 110 h respectively.

A plan to build a net zero energy building in hydrogen and electricity-based energy scenario in South Korea

As net zero energy buildings (NZEBs) are attracting global attention, possible energy transition scenarios for NZEBs have been proposed in South Korea: (1) hydrogen-based or (2) electricity-based energy supply. Compared with a typical Korean residential building that uses a gas-fired boiler and air conditioner, the buildings in the two scenarios can significantly reduce energy consumption and emissions. In this context, this study aims to evaluate the performance of NZEBs in hydrogen- and electricity-based energy-supply scenarios based on simulation. An NZEB is constructed considering passive designs, active systems, and renewable energy systems. Subsequently, its performance is evaluated in terms of energy, environmental, and economic metrics, considering life cycle performance. The evaluation results confirm that the electricity-based energy scenario has better energy and environmental performance than the hydrogen-based energy scenario, with each scenario showing energy savings of 62% and 53%, respectively. In the electricity-based scenario, application of the passive design, active system, and renewable system accounts for savings of 48.2%, 21.2%, and 7.8%, respectively. Consequently, achieving NZEB requires more than 13 photovoltaic panels. In case of economic feasibility, all scenarios have positive operating cost savings. However, scenario 1 shows insufficient economic feasibility owing to high initial investment cost.

Performance of solar-air source heat pump heating system aided by district heat supply network research

Abstract To improve the usage rate of district heat supply network and solve the frost problem in solar-air heat pumps, this study used TRNSYS to construct a new solar-air source heat pump heating composite system that uses waste heat from the district heat supply network. The impact of the waste heat recovery device on the heating performance of the new composite system was analysed, and the economic and environmental performance of the composite system was compared with other heating systems. During a typical day, the average coefficient of performance of air source heat pumps (COP) of the composite system increased by 13% and the power consumption of the system decreased by 35.9%. Throughout the heating season, the power consumption of the composite system was 13.59% higher than that of traditional systems, and system coefficient of performance (SCOP) was 15.89% lower than traditional systems. Based on economic analysis, the relative operating costs of the composite system, coal-fired boiler, gas-fired boiler, oil-fired boiler and combined heat and power (CHP) are 1, 1.19, 2.33, 5.56 and 0.85, respectively. The operating cost of the composite heat source system is only 17.43% higher than that of CHP and lower than the other three heating systems. Quantitative evaluations of the environmental friendliness of these systems were conducted using the fuzzy analysis mathematical method. The evaluation results were 9.62, 5.89, 15.05, 9.10 and 6.79, respectively. It was found that the composite system is second only to the gas-fired boiler in terms of environmental friendliness and is 38.9% higher than the coal-fired boiler and 29.5% higher than the CHP.

Environmental constrained medium-term energy planning: The case study of an Italian university campus as a multi-carrier local energy community

The European Union defined the ambitious carbon-neutrality goal for 2050. Such a transition must be done gradually to avoid huge investments; therefore, medium-term energy planning of energy supply systems must be performed properly considering both economic and environmental aspects. Sector coupling measures aid to achieve this ambitious target, although they require a remarkable financial investment. This paper presents an innovative methodology for the medium-term energy planning of the university campus “Marche Polytechnic University” located in Italy towards the carbon neutrality, i.e., 50 % of carbon emissions reduction by considering financial investment aspects. The university campus is a multi-carrier local energy community with multiple technologies such as photovoltaic, combined heat and power, gas-fired boilers, absorption, and electric chillers that satisfy the end-users’ energy demand. A different mix of installed and new technologies (e.g., energy storage or hydrogen) are investigated through the Calliope framework. The case studies present the economic-based optimal scenario of a typical year planning, guaranteeing the same 50 % carbon emissions reduction. Results underline the importance of exploiting synergies among multiple carriers and the essential role of i) renewables (e.g., additional 3.3 MW of photovoltaic to be installed), ii) batteries with a capacity of 7 MWh, and (iii) sector coupling technologies.

Feasibility study on solar coupled gas-fired boiler heating system retrofit in residential buildings in the HSCW zone of China

Residential buildings in the hot summer and cold winter (HSCW) zone rely on gas-fired boiler for heating have a certain application basis, but high operating costs and limited gas consumption seriously limit the promotion of gas-fired boiler. To reduce domestic gas consumption in Wuhan, two solar auxiliary gas-fired boiler heating systems formed in parallel and series are proposed and explore the feasibility of coupled heating system retrofit. The simulation models of two solar coupled gas-fired boiler heating systems are established by TRNSYS, and the results indicate that the indoor thermal environment of the two systems is good and the temperature of the tank is stable. The solar fraction of the parallel system reaches 24.40%, which has better energy saving. The optimization analyses display that the system has the best economy when the collector area ratio is 10.0%, and the collector area and tank volume ratio is 8/0.7. The solar-assisted parallel heating system retrofit can save 2.02 × 104 MJ over the entire life cycle, and the increased initial investment can be recovered within 4.75 years. The research results can provide a basis and new ideas for the heating retrofit of the gas-fired boiler in residential buildings in the HSCW zone.

ТЕХНОЛОГІЯ ТЕПЛОВОГО ЗАХИСТУ ГАЗОВІДВІДНИХ ТРАКТІВ КОТЕЛЬНИХ УСТАНОВОК

An effective technological solution for thermal protection of the gas-exhaust tract and chimney of gas-fired boiler units against possible condensation is proposed. The principle of the technology is a combination of two-stage deep cooling of exhaust-gases followed by an increase in their temperature in a gas-gas heater.

Design and Experimental Investigation of Novel Flue Gas Condenser

Dünyada ihtiyaç olan enerjinin büyük kısmı halen fosil yakıtlarla sağlanmaktadır. Küresel salgın, savaşlar, doğal afetler vb. sebeplerden dolayı enerji maliyetleri her geçen gün artmaktadır. Bundan dolayı enerji verimli sistemlere rağbet artmaktadır. Bu çalışmada, doğalgaz kaynaklı bir kazanın atık baca gazı ısısı kondenserle geri kazanılmıştır. Öncelikle analitik hesaplamalar ile kondenser boyutlandırılmıştır. Daha verimli ısı geri kazanımı için gövde ve boru tarafında homojen akışkan dağılımı amaçlanmıştır ve bunun için HAD analizleri yürütülerek nihai tasarım, analiz sonuçlarına göre belirlenmiştir. Sonrasında kondenser üzerinde performans deneyleri gerçekleştirilmiş olup, analitik hesaplar ile %94 oranında doğrulanmıştır. Ayrıca nihai tasarımda gövde tarafındaki akışın homojen olduğu termal kamerayla ispatlanmıştır.

Impact of startup and defrosting on the modeling of hybrid systems in building energy simulations

The use of hybrid system (HS) consisting of an air-source heat pump (HP) and gas-fired boiler is spreading, because their installation can mitigate the problems related to HP systems in existing buildings. The efficiency of the HS is strongly affected by the control strategy and size of the heat generators as well as the building characteristics. A coupled building-HVAC simulation is the most effective way to study the influence of these factors. However, the HS model must be simple enough but relevant to actual physical behavior to be fit for purpose. In this regard, reduced generators’ performance during the startup phase and COP degradation due to defrost cycles are often overlooked in energy simulations of building and HVAC systems. This paper introduces new, reliable, and easy-to-compute experimentally derived correlations to consider performance losses due to defrosting cycles and startup phases in building energy simulations. Unlike previous studies, the new correlations consider the dependency of startup losses and duration on the operating conditions. The model is validated by experimental simulation of two load profiles. Experimental data show that the HP under some conditions can take up to 20 min before it comes up to capacity, and during this time the COP degrades to about 15% from the nominal COP.

Energy, exergy, energy-saving, economic and environmental analysis of a micro-gas turbine-PV/T combined cooling, heating and power (CCHP) system under different operation strategies: Transient simulation

A micro-gas turbine (MGT) combined cooling, heating and power system coupled with low concentrating photovoltaic/thermal-heat hump (LCPV/T-HP) and absorption chiller is proposed in this study. LCPV/T is used as the heat source of HP to realize mutual promotion. The performance of CCHP system under different operation strategies is dynamically simulated and analyzed by TRNSYS software from energy, exergy, energy-saving, economy and environment. The results demonstrate that both high temperature water source heat pump (HWHP) and low temperature water source heat pump (LWHP) achieved better COP in following electric load (FEL) mode. The average COP of HWHP and LWHP are 22.69% and 4.75% higher than the rated COP, respectively. Annual total cost per unit building area (ATCUBA) and carbon dioxide emissions per unit building area (CDEUBA) are also more advantageous in FEL mode, while primary energy consumption per unit building area (PECUBA), ATCUBA and CDEUBA seems less preferable in following thermal load (FTL) mode. The exergy efficiency and energy efficiency of the system in FEL mode are 19.96% and 41.90% in summer, and 25.13% and 59.36% in winter. Additionally, the equipment with higher exergy loss is mainly LCPV/T, gas-fired boiler, absorption refrigeration unit, MGT and hot water generator under the three operation strategies.

Experimental study on flow and heat transfer performance of condensing gas-fired boiler

In the process of energy utilization, a large amount of heat transfer needs to be realized through the heat exchange process. Therefore, the development of efficient enhanced heat exchange technology has important theoretical and application value for realizing the efficient utilization of energy and reducing pollutant emissions. Condensing heat exchanger is the core component of condensing water heater. Firstly, this paper analyses the development trend of condensing heat exchanger at home and abroad, and studies the heat exchange, pollutant emission and structural optimization design of condensing heat exchanger by using the gas water heater test-bed. Using the field synergy theory, the flow channel and fin structure of the heat exchanger are optimized. The series flow channel on the water side of the heat exchanger is optimized as the structure of first parallel and then series flow, so that the heat transfer capacity of the water side of the heat exchanger can be increased by 5.6% at the maximum, the reduction of NOx emission concentration is relatively less than 6.7%.

Sustainable opportunities to recover power plants’ waste heat: a benchmark of techno-economically optimized heat pumps

Current climate targets, adopted worldwide, pursue the decarbonization of all energy sectors. In power generation, the spread of RES has caused the shift of the Combined Cycle Gas Turbine (CCGT) power plants’ traditional role from providing constant baseload power to flexible operations providing services and backup capacity to the grid, as a consequence, the revenues opportunities on the traditional electricity markets (e.g., day-ahead, and intra-day markets) are no longer certain. At the same time is urgent to address a significant carbon intensity reduction in the heating sector, which is responsible for a large part of the current greenhouse gas emissions. Exploiting the low-exergy waste heat of CCGT’s water-cooled condenser as a thermal source for vapor compression heat pumps can meet two targets. On one hand, the revenues from heat production enhance the viability of the CCGT power plant, often essential for the security of the electrical supply. On the other hand, the heat delivered to the user represents a low-carbon alternative to traditional gas-fired boilers or even to air-sourced heat pumps characterized by lower efficiency. This work assesses the recovery of thermal energy from the sea cooling water at the bottoming cycle condenser of Tirreno Power 794 MWel CCGT in Vado Ligure through a high-temperature heat pump using R600 as a working fluid. Cooling water represents a privileged heat source and the integration into the power plant’s site allows running the HP at a lower cost than the electricity retail price. The case study takes into account the new Vado Ligure sports hall, to size the HP and explore the economic and environmental performances. The proposed layout is compared with the main solutions available: air source heat pump, gas, and electric boilers. The results show that on a lifespan of 20 years such integration of a heat pump with a CCGT could lead to consistent economical savings and emissions cuts.