燃气锅炉烟气热损失及冷凝余热回收

分析了烟气中水蒸气体积分数、烟气露点的影响因素,探讨了燃气锅炉排烟温度、过剩空气系数对烟气热损失的影响。结合算例,对采用烟气冷凝余热回收装置提高燃气锅炉热效率进行了理论计算。     

Mathematical model of heat transfer and feasibility test of improved cooking stoves in Bangladesh

Improved cooking stoves (ICSs) advance the cooking system significantly in Bangladesh. However, the comparative performance analyses of ICSs of Bangladesh are not available in the literature. In this study, heat loss through the stoves was investigated by using ANSYS simulation. From the simulation result, it was found that the average temperature of the wall of ICSs was less than the conventional stove. The maximum thermal efficiencies of some ICSs were found 30%, which is better than other conventional stoves. In addition to this, a feasibility study of ICSs has been carried out by considering cost, greenhouse gas emission and effectiveness of the ICSs. Taken all into consideration, this study would contribute to the literature for further improvement of the stove and guide the consumer to select the appropriate ICS.     

天然气燃烧烟气的冷凝传热特性

分析了天然气燃烧烟气的冷凝传热过程,综述了烟气冷凝传热的准则。综述了烟气流过管束、高流速、不同空气系数及不同的SO2体积分数等工况下的冷凝传热特性。     

Home interventions are effective at decreasing indoor nitrogen dioxide concentrations

Nitrogen dioxide (NO₂), a by‐product of combustion produced by indoor gas appliances such as cooking stoves, is associated with respiratory symptoms in those with obstructive airways disease. We conducted a three‐armed randomized trial to evaluate the efficacy of interventions aimed at reducing indoor NO₂ concentrations in homes with unvented gas stoves: (i) replacement of existing gas stove with electric stove; (ii) installation of ventilation hood over existing gas stove; and (iii) placement of air purifiers with high‐efficiency particulate air (HEPA) and carbon filters. Home inspection and NO₂ monitoring were conducted at 1 week pre‐intervention and at 1 week and 3 months post‐intervention. Stove replacement resulted in a 51% and 42% decrease in median NO₂ concentration at 3 months of follow‐up in the kitchen and bedroom, respectively (P = 0.01, P = 0.01); air purifier placement resulted in an immediate decrease in median NO₂ concentration in the kitchen (27%, P < 0.01) and bedroom (22%, P = 0.02), but at 3 months, a significant reduction was seen only in the kitchen (20%, P = 0.05). NO₂ concentrations in the kitchen and bedroom did not significantly change following ventilation hood installation. Replacing unvented gas stoves with electric stoves or placement of air purifiers with HEPA and carbon filters can decrease indoor NO₂ concentrations in urban homes.     

Controlling building indoor temperature and reducing heating cost through night heating electric stove

This paper investigates the use of massive electric stove as a thermal storage in order to reduce the heating cost associated with maintaining indoor comfort condition in building. The control of electric stove takes advantage of low night-time electrical rate by shifting heating loads from day-time to night-time. A general numerical modelling of thermal behaviour of building envelope, electric stove and indoor air under the condition of outdoor variation is presented in detail. The resultant non-linear system of the heat balance equations, partial differential equations, is solved numerically. Besides the modelling work, attention is put on the control of electric stove’s night heating in such way that the stove-stored energy is released during day-time without sacrifice of indoor comfort. A simple control algorithm is given. Model applications show that the night heating with a proper size massive electric stove as a building thermal storage is cost-effective for buildings with night electrical rate benefit, while maintaining a comfortable indoor temperature in the building. Simulation also illustrates that up to 28% heating cost saving can be obtained compared with conventional direct heating.     

燃气热水器换热效率的影响因素

对燃气热水器的换热器建立单管计算模型,计算分析了工作参数(烟气进口温度、过剩空气系数、烟气温度分布、水质量流量)、结构参数(肋片数量、肋片厚度)和水管顺、逆流排布对换热器换热效率的影响。     

Mutagenicity assay of emission extracts from wood stoves: comparison with other emission parameters

The emission from wood stoves of several types of air pollutants has been measured under standardized burning conditions with emphasis on the amount of organic compounds and determination of the mutagenic activity with the Salmonella/microsome assay. The study corroborates earlier findings that conventional wood stoves can be a significant source of hydrocarbon and tar compounds in the ambient air. The emission of mutagenic compounds comprise both compounds requiring mammalian activation and compounds which are active in the test without exogenous activation. The mutagenicity tests show that nitroaromatic compounds are present in wood stove emissions, although the emission of nitrogen oxides is low. A wood stove constructed using the downdraft principle emitted much less hydrocarbons and tar, less mutagenic components and slightly less carbon monoxide than conventional wood stoves.     

Household CO and PM measured as part of a review of China's National Improved Stove Program

In 2001-2003, a team of researchers from the United States and China performed an independent, multidisciplinary review of China's National Improved Stove Program carried out since the 1980s. As part of a 3500-household survey, a subsample of 396 rural households were monitored for particulate matter less than 4 microm (PM(4)) in kitchens and living rooms over 24 h, of which 159 were measured in both summer and winter. Carbon monoxide was measured in a 40% subsample. The results of this indoor air quality (IAQ) component indicate that for nearly all household stove or fuel groupings, PM(4) levels were higher than - and sometimes more than twice as high as - the national PM(10) standard for indoor air (150 microg PM(10)/m(3)). If these results are typical, then a large fraction of China's rural population is now chronically exposed to levels of pollution far higher than those determined by the Chinese government to harm human health. Further, we observed highly diverse fuel usage patterns in these regions in China, supporting the observations in the household survey of multiple stoves being present in many kitchens. Improved stoves resulted in reduced PM(4) from biomass fuel combinations, but still not at levels that meet standards, and little improvement was observed in indoor pollution levels when other unimproved stoves were present in the same kitchen. As many households change fuels according to daily and seasonal factors, resulting in different seasonal concentrations in living rooms and kitchens, assessing health implications from fuel use requires longitudinal evaluation of fuel use and IAQ levels, combined with accurate time-activity information. PRACTICAL IMPLICATIONS: Leaving aside the difficult issue of enforcement, it is uncertain whether Chinese household IAQ standards represent realistic objectives for current attainment given current patterns of energy consumption in rural China, which rely so heavily on unprocessed solid fuels. Even when used with chimneys, these fuels emit substantial pollution into the household environment. It is probable that low-emission technologies involving gaseous/liquid fuels or high combustion - efficiency biomass stoves need to be promoted in order to achieve these standards for the greater part of the population.     

LNG空温式气化器管束传热特性

液化天然气(LNG)空温式气化器由翅片管管束组成,以节能环保的优势在LNG中小型气化站得到广泛应用。空温式气化器管束中的单根翅片管传热会受到相邻翅片管的影响,与大空间中的单根翅片管的传热过程存在差异,传统的传热设计中往往忽略管束中翅片管的传热差异,带来较大误差。针对空温式气化器管束传热特性展开研究,对涉及流固耦合传热问题的翅片管管束进行整场建模与求解,采用混合物模型和Lee模型求解管内LNG气化传热,得到了管束中不同位置翅片管的空气侧温度场分布及传热系数,建立了空气侧传热差异系数拟合公式,并用管束空气侧传热特性实验对拟合公式进行了验证。     

催化燃烧锅炉IV+型热效率实验研究

主要研究贫天然气／空气混合气在装有辐射换热器和冷凝换热器的催化燃烧锅炉IV＋型进行催化燃烧的热效率以及冷凝换热器对烟气温度和热效率的影响。对于催化燃烧锅炉IV＋型的热效率实验,得到热效率与水流量的变化关系,总结出催化燃烧锅炉的一些燃烧特性。结合资料探讨了催化剂的失活及其影响因素,介绍了催化剂从生产到回收的流程,并说明了催化剂的再生和重要组分的回收。     

Simple modelling procedure for the indoor thermal environment of highly insulated buildings heated by wood stoves

Space heating using wood stoves is a popular solution in many European countries. The nominal power of the state-of-the-art stoves is oversized compared to the needs of highly insulated buildings, leading to a risk of overheating. A modelling procedure is here developed in order to investigate the indoor thermal environment generated by wood stoves in such buildings. This procedure is kept simple to perform all-year detailed dynamic simulations (e.g. using TRNSYS) at an acceptable computational cost. A specific experimental set-up has been developed for validation, essentially regarding the interaction between the stove and the building. The largest source of error appears to be the thermal stratification in the room where the stove is placed. The experiments prove that the model gives a fair insight into the global thermal comfort. Therefore, it is possible to investigate the conditions required for a stove to be properly integrated in a highly insulated building.     

某工程热风炉扩容改造结构分析

结合工程实例,以某工程热风炉扩容改造为例,综合考虑各方面因素,利用有限元技术对热风炉扩容改造后的炉壳结构进行了整体分析计算,使改造后的热风炉新旧炉壳在扩容增压后均可以安全工作。为热风炉改造扩容设计提供了一种有效的计算方法。     

Particulate matter and carbon monoxide in highland Guatemala: indoor and outdoor levels from traditional and improved wood stoves and gas stoves

Area 22-h average carbon monoxide (CO), total suspended particulates (TSP), particles less than 10 microns in diameter (PM10), and particles less than 2.5 microns in diameter (PM2.5) measurements were made in three test homes of highland rural Guatemala in kitchens, bedrooms, and outdoors on a longitudinal basis, i.e. before and after introduction of potential exposure-reducing interventions. Four cookstove conditions were studied sequentially: background (no stove in use); traditional open woodstove, improved woodstove with flue (plancha), and bottled-gas (LPG) stove. With nine observations each, kitchen PM2.5 levels were 56 micrograms/m3 under background conditions, 528 micrograms/m3 for open fire conditions, 96 micrograms/m3 for plancha conditions, and 57 micrograms/m3 for gas stove conditions. Corresponding PM10/TSP levels were 173/174, 717/836, 210/276, 186/218 micrograms/m3. Corresponding CO levels were 0.2, 5.9, 1.4, 1.2 ppm. Comparisons with other studies in the area indicate that the reductions in indoor concentrations achieved by improved wood-burning stoves deteriorate with stove age. Mother and child personal CO and PM2.5 measurements for each stove condition demonstrate the same trend as area measurements, but with less differentiation.     

A pilot study of traditional indoor biomass cooking and heating in rural Bhutan: gas and particle concentrations and emission rates

Although many studies have reported the health effects of biomass fuels in developing countries, relatively few have quantitatively characterized emissions from biomass stoves during cooking and heating. The aim of this pilot study was to characterize the emission characteristics of different biomass stoves in four rural houses in Bhutan during heating (metal chimney stove), rice cooking (traditional mud stove), fodder preparation (stone tripod stove), and liquor distillation (traditional mud stove). Three stage measurements (before, during, and after the activity had ceased) were conducted for PM_2.5, particle number (PN), CO, and CO₂. When stoves were operated, the pollutant concentrations were significantly elevated above background levels, by an average of 40 and 18 times for PM_2.5 and CO, respectively. Emission rates (mg/min) ranged from 1.07 × 10² (PM_2.5) and 3.50 × 10² (CO) for the stone tripod stove during fodder preparation to 6.20 × 10² (PM_2.5) and 2.22 × 10³ (CO) for the traditional mud stove during liquor distillation. Usable PN data were only available for one house, during heating using a metal chimney stove, which presented an emission rate of 3.24 × 10¹³ particles/min. Interventions to control household air pollution in Bhutan, in order to reduce the health risks associated with cooking and heating, are recommended.     

Experimental study and analysis of air heating system using a parabolic trough solar collector

An experimental study of air heating system was carried out using a parabolic trough collector with a U-tube aluminium heat exchanger. An evacuated tube placed at the focal length of the parabolic trough collected the solar radiations reflected from the surface of parabolic trough. The air was used as a working fluid, which was heated by passing it through a U-shaped aluminium heat exchanger placed inside the evacuated tube. It was found that efficiency of the parabolic trough collector depends on the mass flow rate, solar intensity and use of fins. It was observed that by using fins at a high mass flow rate of 4.557?kg/h, the maximum temperature of 126°C was achieved which is 13.27% more than the maximum temperature obtained without fins. Furthermore, for a low-mass-flow rate of 1.69?kg/h, the maximum temperature obtained was 149°C.     

Identification of empirical transfer function coefficients for a hollow tile based on detailed models of coupled heat transfers

Numerical simulation of transient heat transfer through a hollow tile, two air cells deep, is carried out using the SIMPLE algorithm. The coupling between the heat transfers by conduction, convection and radiation is taken into account. The heat fluxes computed for realistic time-varying excitations are used to derive empirical transfer function coefficients using an identification technique. Dynamic responses of the hollow tile predicted using both the transfer function coefficients and the simulation program are compared for thermal excitations that differ from those used to derive the coefficients. The results show a very good agreement between the two procedures’ predictions.     

天然气烟气冷凝热效率计算及影响因素分析

建立了天然气烟气带冷凝过程热效率计算的数学模型，讨论了排烟温度、空气系数和空气含湿量与热效率的关系，分析了空气预热和补燃对热效率的影响。     

Impacts of stove/fuel use and outdoor air pollution on chemical composition of household particulate matter

Biomass combustion for cooking and heating releases particulate matter (PM_2.5) that contributes to household air pollution. Fuel and stove types affect the chemical composition of household PM, as does infiltration of outdoor PM. Characterization of these impacts can inform future exposure assessments and epidemiologic studies, but is currently limited. In this study, we measured chemical components of PM_2.5 (water-soluble organic matter [WSOM], ions, black carbon, elements, organic tracers) in rural Chinese households using traditional biomass stoves, semi-gasifier stoves with pelletized biomass, and/or non-biomass stoves. We distinguished households using one stove type (traditional, semi-gasifier, or LPG/electric) from those using multiple stoves/fuels. WSOM concentrations were higher in households using only semi-gasifier or traditional stoves (31%-33%) than in those with exclusive LPG/electric stove (13%) or mixed stove use (12%-22%). Inorganic ions comprised 14% of PM in exclusive LPG/electric households, compared to 1%-5% of PM in households using biomass. Total PAH content was much higher in households that used traditional stoves (0.8-2.8 mg/g PM) compared to those that did not (0.1-0.3 mg/g PM). Source apportionment revealed that biomass burning comprised 27%-84% of PM_2.5 in households using biomass. In all samples, identified outdoor sources (vehicles, dust, coal combustion, secondary aerosol) contributed 10%-20% of household PM_2.5.     

Experimental investigation on air heating and natural ventilation of a solar air collector

Solar air collectors are important components for solar energy utilization in green houses. In this paper, experimental studies were carried out regarding to a solar air collector (SAC), for which the length of air channel is 1500 mm, the width is 500 mm, and a variable air channel gap ranges from 100 to 500 mm. In the experiment, the uniform heat flux along the air channel is effected by three electric heating plates, which play a role as solar radiation. It is found that the temperature distribution of air and the induced natural air-flow rate are highly dependent on heat input, inclination angle, channel gap, etc. Experimental results indicate that the optimum inclination angle for the SAC is 45°, under which a maximum natural ventilation rate can be created. Also found is that there exists an appropriate channel length, about 1 m in this study, beyond which the obtained heat and the natural ventilation rate cannot be increased drastically. Higher the volume of air-flow rate through the SAC, lower the temperature difference between inlet and outlet, consequently, it should be balanced between the air temperature rise and a suitable mechanical air-flow rate in order to obtain maximum heat. Additionally, theoretical analysis based on heat balance equations is testified to agree well with experimental results.     

Analysis of wood burning stoves as a supplemental heat source

The use of wood burning stoves as a supplemental residential heat source is examined. Three common types of wood burners are considered: the wood stove, the wood boiler, and the Franklin‐combination stove. The analysis focuses upon three main areas: cost, energy and environmental effects. Indications are that the large scale use of wood as a fuel source is a viable alternative to conventional energy sources in regions having ample forest resources and relatively low population densities.