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PhD defense: Vijay Chauhan

Superheated Steam Scrubbing and Utilization for Power Generation

  • 28.5.2019, 14:00 - 15:00

The PhD defense of Vijay Chauhan will be held on Tuesday the 28th of May at 14:00 in room V102.

Title of thesis: Superheated Steam Scrubbing and Utilization for Power Generation

Candidate: Vijay Chauhan

Date and time: 28th of May 2019 at 14:00

Room: V102

Thesis Committee:
Guðrún Sævarsdóttir, Associate Professor and Supervisor, Reykjavik University
María S. Guðjónsdóttir, Assistant Professor and Supervisor, Reykjavik University
Halldór Pálsson, Professor, University of Iceland

Examiners: 
Oleh Weres, Powerchem, Chemtreat
Bjarni Pálsson, Landsvirkjun, Geothermal Department, R&D Division

Abstract:

Superheated steam from high enthalpy vapor dominated geothermal fields offers an opportunity to extract greater exergy per unit flow with higher thermodynamic output efficiency compared to conventional geothermal wells. The first full scale well drilled with the objective to deliver superheated steam, IDDP-1, produced steam with an enthalpy of > 3070 kJ/kg and pressure up to 15 MPa. Flow rate up to 48 kg s-1 of steam was achieved which might result in power output up to 48 MW. Utilizing the superheated steam, however, faces challenges because of dissolved silica and chloride carried with the superheated steam. The silica that is present in the superheated steam precipitates when lowering down the pressure which can cause scaling. Presence of chloride in steam causes problem related to corrosion if the steam temperature drops below the acid dew point temperature. In order to avoid the corrosion due to the temperature drop, it is, therefore, necessary to do mitigate the impurities before utilization. However, applying traditional methods for mitigation, like wet scrubbing, causes loss in the steam superheat and hence output exergy.
This work aims to develop a method to utilize the superheated steam consisting of high chloride and silica content as experienced in high enthalpy vapor dominated geothermal fields in a more efficient way than is currently available. To achieve this, a step by step approach is followed in this work. The first step aims to study silica particle transport and deposition in superheated steam flow using Computational Fluid Dynamic (CFD). For this, advection-diffusion model based on Euler-Euler approach is implemented using OpenFOAM. The implemented model was validated by experimental measurements for silica particle deposition in superheated steam flow. Experiments were performed to understand the effect of different parameters on particle deposition velocity. The results from the measurements show agreement with the simulated results. An increase in deposition velocity in the diffusion-impaction regime is observed, signifying silica particle agglomeration as an important factor controlling deposition. The second step aims to propose a method for scrubbing acid gas and silica impurities from the steam without loss in its superheat. To achieve scrubbing without loss in superheat, boiling point elevation property of aqueous potassium carbonate solution is exploited. A power cycle utilizing the scrubbing method is proposed while considering the parameters affecting deposition as concluded from the computational study. A comparison study of the thermodynamic performance of the proposed cycle for the case of IDDP-1 well is done where it is compared to that of the cycle utilizing traditional wet scrubbing. Simulation results for the production curve of IDDP-1 well show an increase in utilization efficiency up to 7% and an increase in net work output up to 12% using aqueous potassium carbonate for scrubbing compared to basic wet scrubbing. The third step aims at computational modeling and experimental study on aqueous potassium carbonate droplets in superheated steam to obtain a better understanding of the proposed scrubbing method. For this, a computational model using the Eulerian-Lagrangian approach is developed in OpenFOAM. Effect of injected solution salt concentration on droplet temperature and concentration were studied using model simulation and experiments. Results from the simulations were in accordance with experimental results, where an increase in boiling point elevation with the increase in injected salt solution concentration was observed. The final step aims at performance analysis of the proposed method using experiments for silica scrubbing from superheated steam using aqueous potassium carbonate solution. Measurements for the effect of injected salt solution concentration on scrubbing efficiency and degree of superheat retained while scrubbing are done. Results from the experiments show an increase in the degree of superheat retained and an increase in scrubbing efficiency with increased aqueous salt concentration.
The overall study demonstrates a technique for scrubbing superheated steam using aqueous potassium carbonate. The proposed technique helps in retaining the steam superheat while scrubbing. To study the behavior of the scrubbing medium in the superheated steam, a computational model for simulating salt solution droplets in superheated steam is developed and validated experimentally. In addition, advection-diffusion model is implemented for simulating silica particle deposition in superheated steam flow. The results from the model simulation were validated experimentally.



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