In this study, the variation of steady-state combustion rate (otherwise called normalized burn rate, NBR) with the density, moisture content, and geometry of sawdust, palm fibre and rice husk briquettes, burned in free air was investigated. The quest for alternative fuel for heating and cooking as a result of depletion of fossil fuel and environmental pollution associated with its burning has necessitated the need to improve on the use of loose agro-waste as alternative in Nigeria. Cylindrical briquettes were used through out the experiment except for the effect of geometry where cylindrical briquettes with central hole and cylindrical solid briquettes were used. The briquettes were formed by compression of the pulp in the mould with an Instron compression test machine at a pressure range between 1.5 and 7.5 N mm−2 which formed briquettes with densities between 200 and 500 kg m−3. The results show that the NBR for the three selected briquette samples: wood sawdust, palm fibre, and rice husk, respectively, was found to decrease as the density and moisture content increases. It was observed that hollow briquette had a higher NBR than that of solid briquette of the same pressure and relaxed diameter with sawdust having the highest variation and rice husk the least. The results show that briquettes could be a viable alternative to fuel wood.
In the present study, a dual-pressure organic Rankine cycle (DORC) driven by geothermal hot water for electricity production is developed, investigated and optimized from the energy, exergy and exergoeconomic viewpoint. A parametric study is conducted to determine the effect of high-stage pressure HP P and low-stage pressure LP P variation on the system thermodynamic and exergoeconomic performance. The DORC is further optimized to obtain maximum exergy efficiency optimized design (EEOD case) and minimum product cost optimized design (PCOD case). The exergy efficiency and unit cost of power produced for the optimization of EEOD case and PCOD case are 33.03% and 3.059 cent/kWh, which are 0.3% and 17.4% improvement over base case, respectively. The PCOD case proved to be the best, with respect to minimum unit cost of power produced and net power output over the base case and EEOD case.
From a thermodynamic viewpoint, it is almost possible to utilize all permanent gases as a working fluid for closed-cycle gas turbine energy conversion system. However, this possibility could be limited due to several criteria, some of which are dictated by both technological and economic requirements. This paper provides a risk assessment on possible uncertainties and operational challenges for selected working fluids such as helium, carbon-dioxide, nitrogen and air, which could impact on the closed-cycle gas turbine technology. The risk assessment presented in this paper is described in two parts which include; technological and financial risk. The technological risk gives an assessment on the effect of the selected working fluids on components material technology, turbine entry temperature, and fluid management system while the financial risk aspect gives an assessment in terms of system cost implications influenced by the working fluids and the impact of legislation on investment decision. The overarching discussions from this paper show that helium has an advantage of a possible compact design which could undoubtedly be important cost savings, however, due to government policies on its availability, the operational cost for using helium could make it a huge disadvantage compared with other working fluids discussed in this paper.
In the last few years, one considerable factor for the viability and interest in the closed-cycle gas turbine (GT) systems for nuclear or conventional power plant application is its potential to maintain high cycle performance at varying operating conditions. However, for this potential to be realized, more competitive analysis and understanding of its control strategy are importantly required. In this paper, the iterative procedure for three independent control strategies of a 40 MW single-shaft intercooled-recuperated closed-cycle GT incorporated to a generation IV nuclear reactor is been analyzed and their performance at various operating conditions compared. The rationale behind this analysis was to explore different control strategies and to identify potential limitations using each independent control. The inventory control strategy offered a more viable option for high efficiency at changes in ambient and part-load operations, however, operational limitations in terms of size and pressure of inventory tank, rotational speed for which the centrifugal forces acting on the blade tips could become too high, hence would affect the mechanical integrity and compressor performance. The bypass control responds rapidly to load rejection in the event of loss of grid power. And more interestingly, the results showed the need for a mixed or combined control instead of a single independent technique, which is limited in practice due to operational limits.
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