Modeling of the reactions of a calcium-based sorbent with sulfur dioxide

A mathematical model of calcium sorbent reactions for the simulation of sulfur dioxide reduction from pulverized coal combustion flue gasses was developed, implemented within a numerical code and validated against available measurements under controlled conditions. The model attempts to resemble closely the reactions of calcination, sintering and sulfation occurring during the motion of the sorbent particles in the furnace. The sulfation was based on the partially sintered spheres model (PSSM), coupled with simulated particle calcination and sintering. The complex geometry of the particle was taken into account, with the assumption that it consists of spherical grains in contact with each other. Numerical simulations of drop down tube reactors were performed for both CaCO3 and Ca(OH)(2) sorbent particles and results were compared with experimental data available from the literature. The model of the sorbent reactions will be further used for simulations of desulfurization reactions in turbulent gas-particle flow under coal combustion conditions

Rigid body dynamics in optimization of the machine tool vibroisolation

Modern design of the machine tool treats the suspending parts as a crucial element of the effective vibration isolation. Therefore the suspending items are specifically developed and subjected to extensive tests before being applied on real objects. These elements ensure accurate levelling and appropriate vibration damping. Usually selection of inadequate support element causes intensive disturbing effects in machining. The paper presents dynamics analysis of the machine tool suspended on flexible mountings. The overall analysis is conceived on a rigid body dynamics. This method enables selection of an optimal supporting configuration. Further on such an effective suspension design prevents a need for expensive monitoring of the dynamic characteristics of the mechanical system, i.e. machine tool and supports. The paper explores dynamics of a real, flexibly supported machine tool. Results are obtained with the assistance of the "SUPPORT" software. Finally the theoretical and computational statements are approved throughout extensive site measurements on the machine tool body with appropriate instrumentation

Mathematical modelling and optimisation of lignite and wheat straw co-combustion in 350 MWe boiler furnace

In this paper pulverised lignite-fired 350 MWe boiler furnace is selected for numerical simulations performed by using in-house developed computer code to deepen understanding of complex processes during direct co-firing with wheat straw. The CFD code is significantly upgraded to accommodate simulation of lignite and wheat straw particle reactions and interactions with gas phase, and to allow analysis of particle behavior under real conditions inside the furnace. Parametric analysis is done with emphasis on the thermal share, size and shape of biomass particle, method of biomass feeding into the furnace and the fuel distribution over the burner tiers. In the most favorable co-firing case (with 10% of wheat straw thermal ratio and particle diameter of 500 mu m), the higher furnace exit gas temperature for 8 degrees C and lower NOx emission of 18.2% are achieved, compared with pure lignite combustion case. The optimal co-firing case provides relatively low percentage of wheat straw particles falling into the hopper (9.57%) and relatively high mass burnout of biomass particles at the furnace outlet (91.81%). Non-spherical shape of wheat straw particles is found to affect the fuel trajectories and flame significantly. The results of parametric analysis could support implementation of biomass co-firing technology in existing coal-fired power plants, to increase energy efficiency and mitigate environmental pollutants

Numerical modeling of in-furnace sulfur removal by sorbent injection during pulverized lignite combustion

Results of the study on SO2 reduction in a utility boiler furnace by means of furnace sorbent injection are presented in this paper with analysis of major influential parameters. The Ca-based sorbent injection process in pulverized lignite fired boiler furnace with tangentially arranged burners is simulated. In simulations sorbent particles are distributed among the burner tiers, where they are injected together with coal, and also through sorbent injection ports located above the burners. The sorbent reactions model was adapted to be efficiently implemented in the code for CFD simulations of complex processes considering both the calculation time and the results accuracy. The sorbent particles reaction model was simplified with several assumptions to allow for faster calculations and significantly reduce simulation time without loss in calculation precision during the particle tracking in boiler furnace. Two phase gas-particle flow is modeled, with coal and sorbent particles reactions and interactions with gaseous phase. Test-cases based on fuels with different composition and combustion organization were simulated in details, and results showed that significant increase in reduction of SO2 at furnace exit could be achieved by proper sorbent injection. The sorbent injection locations were analyzed with special care to enable maximum SO2 capture in the case-study furnace under investigated conditions. Most of the test-cases with low SO2 capture had one or more of the following problems: intensive particle sintering, low local temperatures (leading to low calcination rates), or bad particles distribution. Significant SO2 retention was possible when the process was organized in such a way that particles were exposed to optimal temperature range, and injected in the furnace zones with high SO2 concentration simultaneously. It was shown that better results can be achieved by injection of sorbent through multiple burner tiers, with SO2 emission reduction efficiency around 60% at the furnace exit in several well optimized test-cases

Prediction of calcination and sulphation along the sorbent particle trajectories for desulphurisation in coal-fired furnace

The furnace sorbent injection is analysed numerically, focusing on its behaviour, in order to estimate CaCO3 sorbent utilisation. Comprehensive presentation of numerical results and profound analysis are provided to better understand the process under realistic conditions. The boiler load reduction, varied between 70 and 100%, did not disturb the processes in furnace. Insight into individual trajectories and their overall sulphation reveal that reduced load, in these cases, yield somewhat better SO2 reduction. Reactivity of the sorbent particles was better with the boiler load reduction, especially for particles passing near the flame core. The calcination and sulphation of sorbent particles increase with the boiler load decrease, due to the combined influence of extended particle residence time and more favourable reaction conditions. Thus the boiler load reduction can lead to better particle utilisation and higher SO2 capture. The conclusions are limited to the case-study conditions and impose the need for further investigation

Numerical study of co-firing lignite and agricultural biomass in utility boiler under variable operation conditions

The co-combustion of biomass and coal in a utility boiler could provide cleaner power production and ensure sustainable utilization of the solid fuels. This paper aims to numerically investigate complex pro-cesses in the tangentially-fired 900 MWth boiler furnace during direct co-firing of lignite and biomass with 10% thermal share of agricultural residues (wheat straw, corn straw and soybean straw) under vari-able boiler loads (100%, 85% and 70%). Simulations are conducted by means of in-house developed com-puter code, supported by the specially designed user-friendly graphical interface. Co-firing of agricultural residues provides lower pollutant emissions, somewhat higher furnace exit gas temperature and increase in unburnt carbon in bottom/fly ash, compared to the lignite combustion without biomass. Soybean is found to be the most suitable for co-firing regarding its ash melting point, however due to its abundance and availability the wheat straw is selected for this study. Co-combustion at partial boiler loads results in reduction of NOx and SOx up to 34% and 9.5%, respectively. Burners arrangement and furnace aerody-namics affect the abatement of pollutants. This study may help the global effort s in fighting the climate change, efficiently and cost-effectively, thus offering considerable economic and social benefits