Power-Maintaining Effect of Optimized Turbine Inlet Pressure and Well Allocation at the Hatchobaru Power Plant, Japan

Abstract

In the Hatchobaru geothermal field, Japan, we reconsidered the optimum conditions in terms of facilities and reservoirs as a countermeasure for restoring the power output to 110 MWe, because a remarkable power decline had been observed after the commissioning of Unit No.2.

Study on the facilities indicated that the power output could be recovered by more than 5% by reducing the turbine inlet pressure of Unit No.1 from the present value of 6.56 kg/cm2 to 5.0 kg/cm2. The well characteristics had drastically changed compared with the initial well characteristics due to interference within the reservoirs of Unit No.1 and No.2. Reshaping of the turbine nozzle to reduce turbine inlet pressure actually improved the power output of Unit No.1 by 4.8 MWe, from 50.2 MWe to 55.0 MWe, due to increased steam supply from the recovered wells as well as from the existing wells.

In addition, case studies by numerical simulation indicate the optimum allocation of make-up wells to avoid overproduction beyond the power potential of each productive fault, and of reinjection wells so as not to cool production zones. Accordingly, we obtained an optimum scenario for drilling make-up wells and relocating reinjection wells.

Integrated management in terms of facilities and reservoirs is therefore desirable to maintain the power output of geothermal power plants.