Guidelines for optimum gas extraction system selection

The utilization of the geothermal resource for power generation is always related to the presence of non condensable gases, as natural components of the steam. For this reason, it is necessary to remove these elements in order to improve the thermodynamic efficiency of geothermal power plants. In practical applications there are three main equipments for this task, which are: steam ejectors, liquid ring vacuum pumps and compressors, each of them with advantages and disadvantages that should be considered to achieve the best economical benefits from each project. Finding the balance between this variables can become a difficult task and depends on several operational and economical factors. This study is intended to establish the most important parameters and design conditions to determine the optimum equipment for every condition. To achieve this, a model using MatLab and Refprop was created to simulate the thermodynamic relation between the systems involved in the energy conversion process. The main analysis factors in this thesis were: The non condensable gases amount in the steam, condenser and separator pressure, and from economical factors, the steam and electricity price and interest rate. The results showed that the amount of non condensable gases in the steam is the most important factor to determine the optimal gas extraction system. Under this analysis conditions it is recommended from 0[%] to 1,8[%] the use of steam ejectors, from 1,8[%] to 7,3[%] hybrid system and from 7,3[%] to 20[%] LRVP systems. Compressors system does not give optimal result for this analysis range and conditions. Separator pressure also influences the gas extraction system selection. For high separator pressures ejectors are more efficient in gas removal, but when this parameter is reduced LRVP is recommended to achieve better results. Regarding the condenser pressure was possible to determine that for higher vacuum levels ejectors are the best option. However, when this increases hybrid system is the best option for this analysis case. From the economical analysis was possible to conclude that steam price is the most important factor to determine the best gas extraction system, for low steam prices ejectors are the best option and as the price increases hybrid system and LRVP system become a better option. Electricity price impact is reduced in the GES selection; an increase in electricity price will benefit the utilization of ejectors systems. Interest rate showed to have impact in the economical results of the project, but do not influence the behavior between gas extraction systems. Finally Krafla power plant conditions were simulated to determine the best gas extraction system. The results showed that steam ejectors are the best option for this case