OPTIMUM OPERATION FOR DIFFERENT DESIGN CONDITIONS OF A SINGLE PRESSURE HEAT RECOVERY STEAM GENERATOR (HRSG) FOR MINIMUM ENTROPY GENERATION
Heat Recovery Steam Generator (HRSG) is the critical link between the “topping” gas and “bottoming” steam power cycle of a combined power plant. Depending on the mass flow and property of exhaust flue gas from the gas cycle, optimum design and operation, for minimum entropy generation in a single pressure HRSG generating superheated steam is reported in this paper. It shows that an optimum pressure of steam generation exists for minimum entropy generation. The interdependence between the physical size (and hence cost) of different heat transfer components of HRSG with the thermodynamic optimum operation for minimum entropy generation is presented. Optimum pressure of steam generation increases with greater size of super heater, economizer and evaporator up to certain limit, beyond which the increase in optimum saturation pressure is marginal with increase in size of the heat transfer units. However, increasing evaporator size and degree of superheat have the adverse effect of lesser steam generation for a given economizer and super heater for minimum entropy generation.
Design and operation of a heat recovery steam generator with minimum irreversibility
Abstract Thermodynamic analysis based on the minimisation of entropy generation is applied to the optimal design and operation of a heat recovery steam generator (HRSG) generating saturated steam for a combined gas and steam power cycle. The results show that: (i) an optimal saturation temperature exists for least irreversible operation of an existing HRSG with specified exhaust gas from the gas turbine of the ‘topping’ cycle; (ii) operating the HRSG at the maximum load reduces entropy generation; (iii) increase in the number of transfer units of the evaporator or the economiser of the HRSG beyond certain ‘cut-off’ values will have marginal benefit with respect to entropy generation.
Laminar heat or mass transfer in rectangular channels and in cylindrical tubes for fully developed flow: comparison of solutions obtained for various boundary conditions
Abstract A comparison is made of results obtained with various boundary conditions at the wall of the channels. By comparing blood Sherwood numbers for finite wall resistance with those for constant concentration boundary condition only a small variation is found for various points along the blood channel.