燃煤锅炉改烧天然气炉膛吸热量的校核

出于环保考虑,国内一些城市进行了燃煤锅炉烧天然气的改造工作,文章对燃煤锅炉改烧天然气后炉膛吸热量的校核作了介绍。     

Comparative study of different insulating materials for reducing the heat losses in steam pipes: a technical study

An efficiency loss such as heat loss across bare pipe surfaces reduces the available energy to end-uses and increases the burden on boilers to meet the demand. Energy losses create additional stress on the system that accelerates wear and leads to overloading on the system for which it is not originally designed. In the present study, calculations for heat loss and cost of different insulating materials for varied thicknesses were performed for typical location in Jammu and Kashmir, India. The detailed analysis of the heat loss from bare steam pipes was performed with a view to suggest suitable type of insulation to lower the heat loss to acceptable limits, thereby reducing the cost of fuel. The present work provides the detailed study on the heat conduction analysis of steam pipes for different diameters. This analysis includes the heat loss from steam pipes and cost of insulation for different thicknesses of mineral wool, cement and lead, which can be used as the insulating material. The economics of each insulation type is studied, and the analysis indicates that there is an appreciable fuel saving in terms of thermal units.     

Estimation of electrolytic hydrogen production potential in Venezuela from renewable energies

An initial estimation of the potential for hydrogen (H₂) production in Venezuela is made, obtained by water electrolysis using electricity from renewable sources, taking advantage of the great potential of the country for solar, wind and mini hydro energies. For the first two, its potential maps is obtained from insolation and wind speed maps, respectively, prepared from satellite data, and for mini-hydro, the potential is obtained from documentary information. To calculate the amount of H₂ to produce is used the Higher Heating Value, considering the electrolytic system overall efficiency of 75%, including power requirements of the electrolyzer, auxiliary equipment, and system losses. In addition, in the calculation of usable renewable potential are excluded land areas under special administration, marine, lake and urban areas, and other limitations are considered concerning energy conversion efficiencies and useful areas available for the location of the different renewable technologies.     

Optimal control of energy losses in multi-boiler steam systems

This paper describes the development of a mathematical model to determine the optimized energy losses for a set of boilers (with a wide operating margin) supplying a common load. The model can be applied to steam systems that have a group of liquid- or gas-fired shell boilers available for use. The study shows that when the model is applied, the total energy losses of a few boilers working in unison are lower than when a traditional cascade system is used. The differences in energy loss can even reach approximately 12%. The model shows that increasing the heat load from 0 to 30% yields increasing differences in the energy losses between the standard (traditional) and optimized conditions, up to a maximum value of 79 kJ/s. As the steam demand grows from 30 to 100%, the total difference in energy losses between the standard and optimized conditions decreases systematically. When the multi-boiler system operates at full thermal power (100%), there are no differences in the energy losses. The greatest energy loss differences occur in the heat load range from 10 to 80%. There will be a reduction in the primary fuel used by about 40,300 N m³ per year if the model is applied. The optimization system can be put into operation in existing and proposed plants. The payback period on investment for the optimization controller is less than half a year.     

Numerical study of conduction and radiation heat losses from vacuum annulus in parabolic trough receivers

Parabolic trough receiver is a key component to convert solar energy into thermal energy in the parabolic trough solar system. The heat loss of the receiver has an important influence on the thermal efficiency and the operating cost of the power station. In this paper, conduction and radiation heat losses are analyzed respectively to identify the heat loss mechanism of the receiver. A 2-D heat transfer model is established by using the direct simulation Monte Carlo method for rarefied gas flow and heat transfer within the annulus of the receiver to predict the conduction heat loss caused by residual gases. The numerical results conform to the experimental results, and show the temperature of the glass envelope and heat loss for various conditions in detail. The effects of annulus pressure, gas species, temperature of heat transfer fluid, and annulus size on the conduction and radiation heat losses are systematically analyzed. Besides, the main factors that cause heat loss are analyzed, providing a theoretical basis for guiding the improvement of receiver, as well as the operation and maintenance strategy to reduce heat loss.     

The potential for integration of hydrogen for complete energy self-sufficiency in residential buildings with photovoltaic and battery storage systems

This paper presents an analysis of energy production in a pilot building located in Slovenia, which is a typical residential house with an installed photovoltaic (PV) system and pilot battery storage system. Energy management system gathers data from smart meters every 15 min. As the pilot building location is in central Europe, complete energy self-sufficiency cannot be provided. The most problematic period of energy production with photovoltaic systems is winter. Solar radiation during the winter is much lower than in the summer and sometimes snow covers photovoltaic panels and disables energy production. Energy production and energy consumption are analyzed for one year. This study shows that complete self-sufficiency can be achieved by supplementing photovoltaic systems with hydrogen fuel cells. The amount of hydrogen, which would suffice for complete self-sufficiency for the whole period, is calculated according to the analyzed data. A synergy between photovoltaic system and hydrogen fuel cells is a step forward to complete self-sufficiency with renewable energy sources. The share of self-sufficiency of a hybrid PV fuel cell system would be 62.13%, meaning that there is no possibility for complete self-sufficiency from the pilot system. The shortage of hydrogen is 144.24 kg for one year and for achieving complete energy self-sufficiency, PV system should be bigger. A hybrid system with photovoltaic system, battery storage system and hydrogen fuel cells can be a solution for complete self-sufficiency. From an economic point of view, such systems are accessible for commercial use. The initial investment is relatively high, because of the high cost of the hydrogen storage tank.     

Estimation of the potential array output charge in the performance analysis of stand-alone photovoltaic systems without MPPT (Case study: Mediterranean climate)

The potential array output energy, E_P, stated by the Joint Research Centre (JRC) in their European Guidelines for the Assessment of Photovoltaic Plants and the IEC Standard 61724 does not estimate properly the potential array output of stand-alone photovoltaic (SAPV) systems without maximum power point tracker (MPPT) as it is the case for SAPV systems with MPPT and grid connected systems. In this way, the main purpose of this paper is to validate an expression that compromises simplicity and accuracy when estimating the potential array output of SAPV systems without MPPT. This issue can be of high interest to photovoltaic (PV) practitioners and experts as it can improve the analysis performance of this type of systems, helping to discriminate better the different losses in this kind of systems. Furthermore, a study of the array potential estimation through different expressions will be developed in order to evaluate which matches better the array potential output in SAPV system without MPPT. Although the analysis will be focused especially in Mediterranean climates, it will be derived some general conclusions that can be considered in other climates.     

Assessment of the potential improvement due to multiple apertures in central receiver systems with secondary concentrators

When striving for maximum efficiencies in solar thermal central receiver systems (CRS) the use of gas turbines with bottoming cycles is inevitable. Pressurized volumetric receivers have proven their feasibility and good performance, and their integration into gas turbine cycles has been demonstrated. One disadvantage of this system is the necessity to use secondary concentrators. The sunlight has to be concentrated into the relatively small glass windows of the receiver, which leads to a limited view cone. This means that of all the possible heliostat positions around the tower, only those within the ellipse, resulting from the section boundary of the view cone with the ground plane, are usable.For small systems, for which tower costs are small, the resulting heliostat field layout is similar, with or without secondary concentrator. For large systems, which are more cost-effective, tower costs become significant, and the losses due to atmospheric attenuation and spillage dominate over the cosine losses. Thus, the purely North-oriented fields become increasingly sub-optimal.This article shall demonstrate at what power levels this problem can be alleviated by not using a single, North-oriented aperture, but up to six apertures—each of them associated with a separate heliostat field.     

多联产系统中合成气一步法制取二甲醚的热力学分析

二甲醚具有良好的物理化学性质,市场前景广阔,合成气一步法制取工艺因其成本低而受到普遍关注,而多联产系统联产二甲醚可有效降低初投资。构建了合成气一步法制取二甲醚工艺的化学平衡计算模型,研究了在多联产系统中反应温度、压力和原料气配比对二甲醚平衡产率的影响,得到的优化温度为220~260℃,压力为4~6M Pa,使得二甲醚平衡产率取极大值的H2/CO<1,对于晋城9#无烟煤产生的合成气,优化H2/CO是0.75~0.8。     

GIS-based assessment of the biomass potential from phytoremediation of contaminated agricultural land in the Campine region in Belgium

Dedicated energy crop cultivation is expected to be the prevalent form of biomass production for reaching renewable energy targets set by the European Union. However, there are some concerns with regard to its sustainability. This study demonstrates how this problem can be evaded by applying phytoremediation, i.e. the use of plants to remove pollutants from moderately contaminated soils. By selecting the appropriate plants a considerable biomass flow is produced without taking in scarce agricultural land, while simultaneously remediating the soil to levels of contamination below threshold values. Since phytoremediation is only applicable within a limited range of soil pollutant concentrations, the outer values of this range have to be determined at first. Subsequently, a Geographic Information System (GIS) is needed to perform further analyses. The contamination in the region is predicted using GIS, after which the agricultural area is determined that can be committed to energy crop cultivation. This way, the biomass potential and the resulting bioenergy potential from phytoremediation can be assessed. In this paper the Campine region in Belgium, a region diffusely contaminated with heavy metals like cadmium (Cd), is examined. It is illustrated that more than 2000 ha of agricultural land hold Cd concentrations exceeding guide values set by the Flemish Government. However, a large majority of these soils can be remediated by phytoremediation within a reasonable time span of 42 years. Concurrently, a significant amount of biomass is supplied for renewable energy production.