08 Steam raising (boiler operation~design) The tangential pulverized coal firing system of the 2 x 900 MW boilers for the power plant Wai Gao Qiao in Shanghai, PR of China is computationally investigated. Results have indicated that favourable flow and temperature fields are obtained at full load and part load conditions. 04/02945 Compact field separators for the direct steam generation in parabolic trough collectors: An investigation of models Malayeri, M. R. et al. Energy, 2004, 29, (5-6), 653-663. The direct steam generation in parabolic trough collectors is an option to further improve the efficiency and costs of solar thermal power plants. After its operability has been demonstrated, a refined, cost- oriented design of some specific components is in order. One of such components is the separator in the collector field used for the re- circulation mode. This paper presents the first results of an investigation of options for compact and cost effective devices. It outlines the physical mechanisms of phase separation and inspects several models found in the literature for their applicability to the case under study. The focus is on T-junctions, which offer potential cost advantages over more voluminous constructions. 04/02946 Development and test of small-scale batch-fired straw boilers in Denmark Kristensen, E. F. and Kristensen, J. K. Biomass and Bioenergy, 2004, 26, (6), 561-569. In Denmark, government subsidies for the testing and installation of biomass-fired boilers were available for the period from 1995 until 2002. Each boiler type had to pass an official approval test to achieve subsidy. The combustion abilities of the boiler were optimized prior to the test. The main aim of this subsidy was to encourage the development of energy-efficient and environmentally friendly boilers. The scheme was therefore organized in such a way that the greatest subsidies were awarded for boilers with high efficiency and low emissions. This goal has in effect been achieved for batch-fired straw boilers, where the typical efficiency has been increased from about 75% in 1995 to about 87% in 2002. Similarly, the carbon monoxide emissions have been reduced from 5000 ppm (reference value 10% 02) in 1995 to less than 1000 ppm in 2002. These improvements are mainly due to better insulation inside the combustion chamber, more efficient techniques for supplying air to the combustion process, improved cooling of the flue gas, and optimization of the electronic control unit for the air supply. 04/02947 Direct steam generation in parabolic trough concentrators with bimetallic receivers Flores, V. and Almanza, R. Energy, 2004, 29, (5-6), 645-651. This document shows the results obtained in direct steam generation for low powers in parabolic trough concentrators with bimetallic Cu-Fe wall receivers. The objective is to study its thermal behaviour under transient conditions and stratified two-phase flow. Experimental results in transient state appear considering the variants of mass flows between 60 and 150 kg/h, the direction of the solar beam irradiance on the receiver is from below and on one side of the receiver, this last being the most critical, in particular in steel receivers because of low thermal conductivity. Some conclusions in this work are that the most significant deformation is in a transient state and it happens only in one part of the receiver, when it changes from the liquid phase to the steam phase during the boiling process. The bimetallic receiver reduced the transient deformation to the degree that it does not seem a problem for some critical parts of the absorber system during the direct steam generation (DSG). Whereas in steel receivers the deformation rises to 7 cm, in the Cu-Fe receivers the most drastic deformation was only of 18 mm upwards with a mass flow of 150 kg/h and wall temperature of 200°C. So, the use of the bimetallic receiver is recommended for the DSG for low power applications. 04/02948 Direct steam generation in parabolic troughs: Final results and conclusions of the DISS project Zarza, E. et al. Energy, 2004, 29, (5-6), 635-644. This paper presents a summary of the main results and conclusions achieved in the DISS (Direct Solar Steam) project. The test facility implemented at the Plataforma Solar de Almerfa (PSA) in 1997-8, the so-called PSA DISS test facility, was operated for more than 3000 h in 1999-2000 and 2001 to investigate the direct steam generation (DSG) process under real solar conditions. The feasibility of the DSG process in horizontal parabolic trough collectors has been proven and an important know how has been acquired by the project partners regarding the thermo-hydraulic parameters of the water/steam flow in DSG solar fields. 04/02949 Experimental studies of a biomass boiler suitable for small district heating systems Lundgren, J. et al. Biomass and Bioenergy, 2004, 26, (5), 443-453. Extensive experiments have been carried out in a newly developed furnace suitable for small district heating networks. The fuel is wood- chips with moisture content in the range of 30-58%. One of the unique features of this new furnace is the broad thermal output span, which makes it possible to run the boiler down to 10% of maximum heat load, with maintained low emissions of CO and total hydrocarbons (THC). The aim of this study has been to evaluate the performance of the combustion chamber during steady-state operation in the complete thermal output range. The experiments show very good results over the entire thermal output range. In the range 60kW up to 500kW, the average CO content in the stack gases is typically below 25 mg N m -3 (20 ppm) and the NOx concentration below 195mgNm 3 (95ppm) during steady state conditions. At lower thermal outputs, the average CO content is below 105 mg N m -3 (84ppm). (All values standardized to 10 vol% 02.), 04/02950 In service embrittlement of cast 20Cr32Ni1Nb components used in steam reformer applications Knowles, D. M. et al. International Journal of Pressure Vessels and Piping, 2004, 81, (6), 499-506. Severe embrittlement has been experienced in a number of cast manifold components. This has manifested itself as cracking at tee to manifold connections. Attempts to weld repair proved futile leading to concern about the integrity of the entire system. This experience contrasts with similar components that have successfully remained in service for many years. The paper describes the investigations into these failures and laboratory investigations into the properties of cast 20Cr32Ni1Nb alloys. Results indicate that variations in alloy chemistry within the stated allowable range are sufficient to cause embrittlement. 04/02951 Maximum temperature difference in horizontal and tilted absorber pipes with direct steam generation Eck, M. et al. Energy, 2004, 29, (5-6), 665 676. The direct steam generation (DSG) in parabolic trough collectors is a promising option for the improvement of the reliable parabolic trough technology for solar thermal electricity generation. The DISS (Direct Solar Steam) test facility at the Plataforma Solar de Almerfa is a full- scale solar steam generator consisting of parabolic trough collectors, used to investigate the DSG process under real operating conditions. According to theory and results from lab-scale experiments it was expected that the tilt of the absorber tubes can improve the thermo- hydraulic behaviour of the DSG process significantly. Within the DISS project a test campaign has been performed to investigate the influence of tilt. The evaluation of the test data showed, that the horizontal absorber tube guarantees sufficient cooling confirmed by low tem- perature differences even at very high steam qualities. 04/02952 Measurements and numerical simulations for optimization of the combustion process in a utility boiler Vikhansky, A. et al. International Journal of Energy Research, 2004, 28, (5), 391-401. A three-dimensional computational fluid dynamics code was used to analyse the performance of 550MW pulverized coal combustion opposite a wall-fired boiler (of IEC) at different operation modes. The main objective of this study was to prove that connecting plant measurements with three-dimensional furnace modelling is a cost- effective method for design, optimization and problem solving in power plant operation. Heat flux results from calculations were compared with measurements in the boiler and showed good agreement. Consequently, the code was used to study hydrodynamic aspects of air-flue gases mixing in the upper part of the boiler. It was demonstrated that effective mixing between flue gases and overfire air is of essential importance for CO reburning. From our complemen- tary experimental-numerical effort, IEC considers a possibility to improve the boiler performance by replacing the existing OFA nozzles by those with higher penetration depth of the air jets, with the aim to ensure proper mixing to achieve better CO reburning. 04/02953 Mechanical properties and non-destructive evaluation of chromium-molybdenum ferritic steels for steam generator application Raj, B. et al. International Journal of Pressure Vessels and Piping, 2004, 81, (6), 521-534. The paper presents high temperature mechanical properties and non- destructive evaluation (NDE) of chromium-molybdenum (Cr-Mo) ferritic steels widely used as structural materials for steam generator (SG) applications. Creep and low cycle fatigue deformation and damage (the important design considerations for SGs) of ferritic steels are presented. Recent trend and advances in ferritic steels for SG applications are discussed. The paper also highlights the recent results obtained on creep and fatigue properties of indigenously developed steels. Weld and weld joints of ferritic steels are known to be the weak links affecting the life of the components. The creep properties of weld joints are presented. Apart from mechanical behaviour of ferritic steels, the paper deals with some of the recent results on the 416 Fuel and Energy Abstracts November 2004