PreFEED Optimisation of Hydrostor’s A-CAES System

Objective

Hydrostor, a leading energy storage company, engaged io consulting to optimise its Advanced Compressed Air Energy Storage (A-CAES) system at a PreFEED level. The goal was to enhance system efficiency, reduce capital costs, and establish a robust design basis for future large-scale projects. (image courtesy of Hydrostor Inc.)

Project Scope

The PreFEED Optimisation Study (PFOS) was conducted in four phases:

1. Phase 1 – Focused on optimising the Thermal Management System and heat exchanger selection.
2. Phase 2 – Evaluated turbomachinery configurations and their economic scalability.
3. Phase 3 – Identified key cost reduction opportunities, particularly in heat exchanger performance and efficiency trade-offs.
4. Phase 4 – Assessed alternative turbomachinery options and refined system designs for improved performance and cost-effectiveness.

Key activities included system engineering, technical modelling, thermal management assessment, material selection and constructability analysis.

Findings & Recommendations

Findings

• Thermal Management System Optimisation: Selection of demineralised water over thermal oil significantly reduced lifecycle costs.
• Heat Exchanger Selection: Traditional shell-and-tube heat exchangers provided the best trade-off between cost, durability, and thermal performance.
• Turbomachinery Selection & Performance: The choice of turbomachinery significantly impacted overall plant efficiency and CAPEX.
• System Engineering & Cost Optimisation: Reducing the round-trip efficiency (RTE) target by 5% allowed significant cost savings while maintaining market competitiveness.
• Cavern & Topsides Integration: Managing compensation water quality was critical to system longevity and performance.
• Constructability & Large-Diameter Piping: Large-scale A-CAES plants required innovative construction approaches due to oversized piping.
• Champagne Effect & Cavern Overcharge Risk: A champagne effect (rapid air release due to overcharge) could lead to system failure, posing a significant risk to A-CAES operations.
  • Solution Developed by io & Hydrostor: io, in collaboration with Hydrostor, developed a patented solution (led by Craig Branch) to eliminate the risk of champagne effect through an innovative passive design. This system prevents uncontrolled air loss by ensuring stable air-water interface control within the cavern, mitigating the potential for sudden gas release.

Recommendations

1. Thermal Management System Optimisation: Use site-erected flat-bottomed tanks for water storage and pressurised spheres for hot water storage to balance cost and efficiency.
2. Heat Exchanger Selection: While compact exchangers (e.g., welded plate or printed circuit designs) were evaluated, their cost advantage was marginal. Hydrostor should monitor emerging heat exchanger technologies for future optimisation.
3. Turbomachinery Selection & Performance: Larger-scale, high-efficiency compression and expansion systems were found to reduce unit costs and improve energy recovery. Optimising component selection and system integration was critical to maximising round-trip efficiency while minimising capital expenditure. Further supplier engagement could yield additional competitive alternatives.
4. System Engineering & Cost Optimisation: Prioritise efficient component selection to achieve optimal RTE at the lowest CAPEX, particularly in heat exchanger and compression system design.
5. Cavern & Topsides Integration: Implement a three-tier algae control strategy (circulation, ultrasound, and chemical treatment) to mitigate biological risks.
6. Constructability & Large-Diameter Piping: Prefabrication and modularisation of pipe tracks and structural elements should be maximised to reduce costs and installation time.
7. Champagne Effect & Cavern Overcharge Risk: Implement the patented solution across future A-CAES facilities to enhance operational stability and protect stored energy assets.