Boiler Thermal Efficiency Research Articles

Study on Prediction Model for Boiler Thermal Efficiency Based on Support Vector Regression and Particle Swarm Optimization

Aiming at the problem that the boiler thermal efficiency can't be on-line calculated in the field, data collected are divided into training data and testing data by researching on the 1000MW unit of Sanbaimen Power Plant in Datang Chaozhou, and then prediction model for boiler thermal efficiency is established by applying support vector regression and particle swarm optimization. This method uses optimization function of particle swarm algorithm to optimize the parameters C and g of the prediction model, and applys test data and the randon data to test the model's accuracy and generalization capability. The simulation results show that prediction model for boiler thermal efficiency has higher pre- diction accuracy that relative error is controlled within 1% and has better generalization ability, which provides feasible scheme for online measurement of boiler thermal efficiency.

On-line monitoring of ash fouling and soot-blowing optimization for convective heat exchanger in coal-fired power plant boiler

This paper presented a comprehensive approach of on-line monitoring and optimization for the soot-blowing system in coal-fired power plant boilers. Due to ash fouling monitoring of heat transfer surfaces of the boiler based on dynamic mass and energy balance method, on-line calculation of boiler thermal efficiency and soft measurements for gas flow rate at the double breezing tail and steam flow rate of reheaters, the performance of boiler's soot-blowing system can be evaluated on-line. And then, the suitable soot-blowing strategies are developed for soot-blowing frequencies and duration optimization. Monitoring results and analysis of an experimental application are given to illustrate the proposed methodologies. The methods proposed in this paper can be applied to state assessment and guidance of soot-blowing operation of boiler's soot-blowing system in order to achieve the purpose of energy conservation, without demanding special instruments or complex computing systems.

New configurations of a heat recovery absorption heat pump integrated with a natural gas boiler for boiler efficiency improvement

Conventional natural gas-fired boilers exhaust flue gas direct to the atmosphere at 150–200°C, which, at such temperatures, contains large amount of energy and results in relatively low thermal efficiency ranging from 70% to 80%. Although condensing boilers for recovering the heat in the flue gas have been developed over the past 40years, their present market share is still less than 25%. The major reason for this relatively slow acceptance is the limited improvement in the thermal efficiency of condensing boilers. In the condensing boiler, the temperature of the hot water return at the range of 50–60°C, which is used to cool the flue gas, is very close to the dew point of the water vapor in the flue gas. Therefore, the latent heat, the majority of the waste heat in the flue gas, which is contained in the water vapor, cannot be recovered. This paper presents a new approach to improve boiler thermal efficiency by integrating absorption heat pumps with natural gas boilers for waste heat recovery (HRAHP). Three configurations of HRAHPs are introduced and discussed. The three configurations are modeled in detail to illustrate the significant thermal efficiency improvement they attain. Further, for conceptual proof and validation, an existing hot water-driven absorption chiller is operated as a heat pump at operating conditions similar to one of the devised configurations. An overall system performance and economic analysis are provided for decision-making and as evidence of the potential benefits. These three configurations of HRAHP provide a pathway to achieving realistic high-efficiency natural gas boilers for applications with process fluid return temperatures higher than or close to the dew point of the water vapor in the flue gas.

Impact of Changing Combustion of Shenhua Coal to Boiler Operation

Experimental study of changing and blending combustion of Shenhua coal on boiler operation was carried out, while the furnace slagging during the experiment, the coal pulverizing system adjustment and the boiler operation oxygen control issues were analyzed. The results show that: the boiler can operate in safety blending Shenhua coal and Zhungeer coal with the ratio of 7:3 based on the strengthening laboratory analysis of coal as fired, the safety and economy of the boiler and coal pulverizing system can be ensured with the pulverized coal fineness R90 in 30%, and selecting the lower mill combinations and setting the coal pulverizer outlet temperature at 73°C, the reasonable exhaust gas oxygen content should be 4.0%, and the boiler thermal efficiency has an 1% increase compared with the condiation of burning inferior Shanxi bituminous coal, the nitrogen oxide emissions are significantly reduced.

The Analysis between Two Different Methods of Power Plant Boiler Thermal Efficiency

The power plant boiler is one of the most important facilities in thermal power plants. The thermal efficiency of power plant boilers is the index. This paper discusses the relationship between the boiler thermal efficiency and the coefficient of excess air via two methods, one is called the simplified calculating formula and the other is the calculating formula according to the The People's Republic of China national standard power plant boiler performance test procedures. According to the proposed methods, by solving the same optimal problem, optimum excess air coefficients are obtained. Then a comparative analysis is given. Moreover, an improved way for saving calculation time to get the coefficients of the mixed coal in the so called simplified calculating formula is developed.

Discussion and Analysis on Effect of Hot Secondary Air Governance Gypsum Rain on the Power Plant Unit

For gypsum rain phenomenon in limestone-gypsum wet desulfurization system. This article made programme that has used unit existing equipment allowance. Extracted hot secondary air to heat purified flue gas to eliminate "gypsum rain". This programme is implemented which makes temperature of purified flue gas rising to 70 °C. That almost eliminate "gypsum rain" phenomenon. While temperature of boiler exhaust gas declined, and temperature of hot air reduced, and boiler thermal efficiency declined, unit of power coal consumption rosed. Comparing to other programmes, this programme has a larger advantage in technology, economic, and security aspects.

An environment friendly and efficient lignite-fired power generation process based on a boiler with an open pulverizing system and the recovery of water from mill-exhaust

This paper advances a novel lignite-fired power generation process based on a OPSB (boiler with an open pulverizing system) and the recovery of water from mill-exhaust after the comprehensive analysis of the open pulverizing system used for high-moisture coals and heat/water recovery from boiler exhaust. Then, the thermal calculation method that applies to OPSB is presented based on heat and mass balance analyses of the boiler. Finally, an efficient unit applying the OPSB process is compared with a conventional 600 MW lignite-fired power unit, and the performance of the efficient unit is calculated and discussed in detail. The results show that the efficient unit not only yields a notable increase in the boiler's (2.6%) and the power plant's (1.3%) thermal efficiency but also provides a remarkable advantage in water recovery due to the mass of water vapor concentrated in mill-exhaust. In the efficient unit, the volume fraction of water vapor in mill-exhaust reaches 34%, the water reclaimed from mill-exhaust is so much that a lignite-fired power plant with zero water consumption can be expected, while the pollutant emissions can be reduced in proportion to the increase in boiler thermal efficiency.

A two-tier approach to the data-driven modeling on thermal efficiency of a BFG/coal co-firing boiler

Even though ratio of air to fuel is the major factor in determining the thermal efficiency of a boiler, how to optimize the ratio in the real operation is still more like art than science, especially for a gas/solid multi-fuel combustion system. This study, taking operation data from a real gas/solid fuels co-firing boiler, is aimed to develop the thermal efficiency model. To cope with the complexity of combustion mechanism in a co-firing boiler, this study proposed a two-tier approach to modeling thermal efficiency. The first tier is to transform the plant input variables into the derived variables, which are physically and statistically meaningful to the model-building. In the second tier, this study proposed an adaptive modeling approach by employing nonnegative garrote variable selection and auto-regression integrated moving average correction. Both approaches are first time proposed in building the thermal efficiency model for boilers. The prediction error of boiler thermal efficiency made by the acquired model reaches less than 0.03%. The high accuracy of the proposed modeling approaches makes the implementation of the model-based control of ratio of air to fuel for improving boiler’s efficiency readily practicable.

The Research and Application of Utility Boiler Energy Efficiency Test System

In order to improve identification of new products, we study the energy efficiency test of utility boilers. According to related protocols and test method of the current boiler energy efficiency, we build up the model of boiler thermal efficiency test in direct and indirect procedure. During the procedure, we analysis some key issues such as the blended fuel problem and the desulfurizer’s effect on energy efficiency. On this basis, we develop the Utility Boiler Thermal Efficiency Test System, which is used in boiler industry and achieves the intended purpose.

The Research and Application of Industrial Boiler Energy Efficiency Test System

In order to improve identification of new products, we study the energy efficiency test of industrial boilers. According to related protocols and test method of the current boiler energy efficiency, we put forward an effective solution of new boiler products based on indirect procedure. We build up the model of boiler thermal efficiency test in direct and indirect procedure and analysis some key problems in indirect procedure. On this basis, we develop the Industrial Boiler Thermal Efficiency Test System, which is used in boiler industry and achieves the intended purpose.

Development of a test facility to evaluate performance of a domestic wood pellet boiler

Wood pellet is solid biomass energy and one of renewable energy sources. In 2008, new and renewable energy (NRE) portion is 2.4% with respect to total primary energy in Korea. Korea government wants to increase new and renewable energy portion up to 6.1% by 2020 [1]. To achieve the target of NRE portion, Korea government has been establishing some policies, such as incentive policy, NRE mandatory use for public building and renewable portfolio standard (RPS) and so on. One of these policies is a domestic wood pellet boiler supply policy. But wood pellet boiler manufacturers who want to participate in the supply policy need a performance test result from a qualified test institute such as Korea Institute of Energy Research (KIER) and Korea Testing Laboratory (KTL). So we install a test facility to evaluate heating performance of a domestic wood pellet boiler semi-automatically.In order to achieve a thermal efficiency of a wood pellet boiler, it is very important to maintain heating water inlet and outlet temperature and water flow rate to be stable. We use 2 water passages in the system; one is circulation of a wood pellet boiler heating water passage and the other is a cooling circulation for removal heat from the wood pellet boiler. These 2 water passages exchange heat by a plate type heat exchanger. We control the flow rate of cooling water based on the wood pellet boiler water inlet temperature. With this system, temperature variation of boiler inlet and outlet temperature is less than 0.4 °C, that is ±0.2 °C which is important to evaluate boiler thermal efficiency.

Real-time online monitoring of thermal efficiency in coal-fired power plant boiler based on coal heating value identification

This paper presents a comprehensive real-time online calculation model of coal-fired boiler thermal efficiency based on the low heating value identification of the coal. At first, online calculation approach is proposed to overcome the difficulty that the coal qualities into furnace are often changing and not well obtained real-time, by means of the dynamic mass and energy balance method. Secondly, the excess air coefficient and unburned carbon in fly ash which are the important parameters to calculate the boiler thermal efficiency are determined by soft measurement methods. The paper illustrates the effectiveness of the models as well as the validation of the online simulation, starting from real operation data. The outcome is that it is possible to significantly satisfy the accuracy of online identification of the low heating value (LHV) of the coal into the boiler, and the real-time of online calculations provided by indirect heat balance method. The models can be used to the real-time control and optimisation of the coal-fired utility boilers.

Energy Analysis of Baby Boiler for Steaming of Raw Cashew Nut Seeds

The steaming of raw cashew seeds prior to shelling is adopted widely in small-scale cashew nut processing mills with the help of baby boiler. The wide variations in energy intensity of these mills reveal the scope for energy conservation. The baby boiler coupled with cooker commonly used for steaming of raw seeds was evaluated. The variation in steam pressure, temperature and operating time with respect to fuel was observed along with thermal efficiency of a boiler. The energy intensity to produce the steam using different fuel sources determined. The study revealed that the thermal efficiency of boiler using electricity as a fuel was higher (69.31%) as compared to 4.66% (Wood) and 4.47% (Cashew nut shell). It was observed that, the energy consumed per kg of cashew nut steaming using electricity (248.99 kJ/kg) was minimum followed by wood (3829.96 kJ/kg) and cashew nut shell (3835.64 kJ/kg). The variation of energy consumption for cashew nut steaming revealed the scope for energy conservation in biomass combustion system. The improvement in the biomass combustion efficiency for steam generation could results in less fuel consumption and shorter period.

Combustion and emission characteristics of a domestic boiler fired with pellets of pine, industrial wood wastes and peach stones

This study evaluates the combustion and emission characteristics of a domestic boiler fired with pellets of pine, industrial wood wastes and peach stones. Initially, the boiler performance, firing pine pellets, was evaluated as a function of the thermal input. Subsequently, the influence of the pellets type on boiler performance was also examined. The results reveal that the type of pellets affects significantly the boiler emissions characteristics, with the pine pellets performing significantly better than the pellets of industrial wood wastes and peach stones. The boiler thermal efficiency is not negatively affected when fired with the pellets of industrial wood wastes and peach stones. Typical operating conditions of the boiler are not suitable for the use of wood wastes and peach stones pellets as CO and HC emissions are superior. The pellets of industrial wood wastes and peach stones have, however, an attractive potential for use in domestic boilers, through the optimization of the boiler operating conditions, being this a sustainable means of energetic valorisation of residues with no specific use.

The Integrated Analysis of Economy and Safety on SOFA Running Mode of a 600MWe Boiler

The application of separated over-fire air (SOFA) in coal-fired boiler results in significant decrease of NOx emission but increases the trend of fireside water wall high temperature corrosion and incomplete combustion of pulverized coal. In order to meet the balance between low NOx emission and high boiler thermal efficiency, the main factors of air staging including SOFA flow, SOFA jet velocity and SOFA jet height were experimented on a 600MWe boiler. At the same time, the main components of flue gas beside the water wall were measured to evaluate the trend of high temperature corrosion. By comprehensive analysis, the optimum running mode of SOFA is concluded: (a) 75% of normal SOFA flow is suggested to reduce the trend of high temperature corrosion; (b) higher SOFA velocity is better for higher boiler thermal efficiency; (c) higher SOFA jet height is beneficial to the reduction of NOx emission.

Principles of optimization of combustion by radiant energy signal and its application in a 660 MWe down- and coal-fired boiler

For the optimization of combustion in utility coal-fired boilers, a simple analytic model was set up to relate the radiant energy signal (RES) with the combustion rate (heat release rate) based on the heat transfer equation inside a boiler furnace. It was pointed out that as the air flow rate into the furnace changes, the highest RES corresponds to the highest efficiency, making RES a sensitive quantity for optimization of combustion in boilers. Experiments carried out in a 660 MW down- and coal-fired utility boiler confirmed the characteristics of RES as an indicator of combustion rate inside the furnace and its ability to reflect the boiler thermal efficiency varied with the air flow rate. The utilization of RES in the optimization of combustion can generally improve the boiler thermal efficiency at different unit loads, and the efficiency was raised about 1.0% especially at the rated and lower unit loads. It should be stated that except the lower unit load, the NOx emission from the boiler after optimization of combustion by RES would increase due to the limitation in supply of adequate air flow rate into the boiler, and some new combustion technologies are now available to solve the contradiction.

Development of fuzzy based methodology to commission co-combustion of unprepared biomass on chain grate stoker fired boilers

AbstractThis paper describes the development of an intelligent commissioning system to enable operators to maximise the utilisation of unprepared biomass by combusting the biomass with the minimum amount of support fuel to achieve a desired boiler output and thermal efficiency on chain grate stoker fired boilers. Tests were conducted on a 0·8 MWth chain grate stoker fired hot water boiler to investigate the combustion of different types of biomass blended with a support fuel over a wide range of boiler operating conditions and biomass moisture contents. The commissioning system was developed using fuzzy logic and expert system type rules developed while gathering the experimental data. The system was validated on untested blends of unprepared biomass with two support fuels where it was shown that it is possible to efficiently burn unprepared, high moisture content biomass with a support fuel on a chain grate stoker. This system could enable operators of chain grate stoker fired boilers to maximise the use...

Combustion and NO x emission characteristics of a retrofitted down-fired 660 MW e utility boiler at different loads

Industrial experiments were performed for a retrofitted 660 MW e full-scale down-fired boiler. Measurements of ignition of the primary air/fuel mixture flow, the gas temperature distribution of the furnace and the gas components in the furnace were conducted at loads of 660, 550 and 330 MW e. With decreasing load, the gas temperature decreases and the ignition position of the primary coal/air flow becomes farther along the axis of the fuel-rich pipe in the burner region under the arches. The furnace temperature also decreases with decreasing load, as does the difference between the temperatures in the burning region and the lower position of the burnout region. With decreasing load, the exhaust gas temperature decreases from 129.8 °C to 114.3 °C, while NO x emissions decrease from 2448 to 1610 mg/m 3. All three loads result in low carbon content in fly ash and great boiler thermal efficiency higher than 92%. Compared with the case of 660 MW e before retrofit, the exhaust gas temperature decreased from 136 to 129.8 °C, the carbon content in the fly ash decreased from 9.55% to 2.43% and the boiler efficiency increased from 84.54% to 93.66%.

Improved NOxEmissions and Combustion Characteristics for a Retrofitted Down-fired 300-MWeUtility Boiler

A new technique combining high boiler efficiency and low-NO(x) emissions was employed in a 300MWe down-fired boiler as an economical means to reduce NO(x) emissions in down-fired boilers burning low-volatile coals. Experiments were conducted on this boiler after the retrofit with measurements taken of gas temperature distributions along the primary air and coal mixture flows and in the furnace, furnace temperatures along the main axis and gas concentrations such as O(2), CO and NO(x) in the near-wall region. Data were compared with those obtained before the retrofit and verified that by applying the combined technique, gas temperature distributions in the furnace become more reasonable. Peak temperatures were lowered from the upper furnace to the lower furnace and flame stability was improved. Despite burning low-volatile coals, NO(x) emissions can be lowered by as much as 50% without increasing the levels of unburnt carbon in fly ash and reducing boiler thermal efficiency.

Full-scale co-firing trial tests of sawdust and bio-waste in pulverized coal-fired 230t/h steam boiler

Abstract Co-firing trial tests of sawdust and bio-waste coming from cereal production with hard coal were carried out at Skawina Power Plant in Poland (1532 MW in fuel, currently belonging to CEZ Group). Skawina Power Plant is a tangentially-fired pulverized coal unit with nine boilers (4 boilers of 210 t/h and five boilers of 230 t/h live steam respectively) that produces 590 MW electricity and 618 MW of heat (district heating and process steam). The paper presents an analysis of energy and ecological effects of sawdust and bio-waste co-firing in the existing pulverized hard coal boiler. The mixture of coal and biomass was blended in the coal yard, and fed into the boiler through the coal mills. During the tests, combustion of mixtures composed of hard coal and sawdust (with mass share of 9.5%) and hard coal – bio-waste (6.6% mass basis) were examined. The co-firing tests were successful. Based on the analysis of the test results, the influence of biomass co-firing on specific components of energy balance (e.g. stack losses and boiler thermal efficiency) was discussed, in comparison to combustion of coal alone. The emission indices during coal combustion were calculated and compared to the emission indices for biomass co-firing. It was proved that co-firing of both biomass sorts leads to a decrease of CO and SO 2 emissions. Due to the possibility of considering the part of the energy generated during biomass co-firing as renewable energy, the procedure for biomass based renewable energy share determination is presented and illustrated with an example.