Tasks: 

1. Prepare a simple block flow diagram (no loops) for a process that stores renewably generated electricity as compressed hydrogen and recovers electricity back again from the stored hydrogen. Think about what unit operations you need to do, to achieve this.

Your process uses a feed of seawater at (20°C, 1 at m) which is used to produce hydrogen gas via electrolysis (operates at 50oC  30 bar, 80% water splitting energy efficiency). This hydrogen gas product is then further processed to produce a stream of compressed hydrogen (400 bar). The hydrogen is stored in a solution-mined salt cavern deep underground, during which time its temperature equilibrates with the surroundings to 40oC. After being stored until required, the hydrogen is depressurised and used as fuel in an open Brayt on cycle to regenerate electricity.

Show any waste streams, the main unit operations and the main heat and work flows on your BFD.

2. Estimate the main mass, heat and work flows for the process and hence the overall energy efficiency of the system as an energy storage.  

For now, assume that the thermal efficiency of the Brayton cycle is 33%. We will relax this assumption in week 9. You may also assume for now that all gases behave ideally and that any compressors or expanders used are is entoopic (reversible). 

3. Your submitted report should be no longer than four pages (including any title page, and citations for sources used). Include your block flow diagram, and brief calculations to support your calculated energy efficiency. Briefly explain the main sources of energy loss and whether the process could be improved to  minimise them. Don’t spend more than a few hours on this including your class time – it’s not meant to be a polished assignment. 

4. After submitting the assignment in moodle, every member of the team be sure to complete peer evaluation using the assignment tool