Since the Aguirre Power Plant (Figure 1), owned by the Puerto Rico Electric Power Authority (PREPA), provides electricity to one third of Puerto Ricans, effective and efficient operation is essential to meet the demand. Hence, the plant uses an on-site hydrogen generator as a replacement to its stored hydrogen supply in order to produce electricity in a safer and more economical way.
Figure 1. The Aguirre Power Plant uses all the latest technologies, such as on-site hydrogen generators, to cost-effectively produce electricity for its customers.
Risks, Hassles and Expenses Associated with Stored Gas
Until May 2010, the Aguirre Power Plant used stored hydrogen to cool its two 450MW generators. For this purpose, the plant spent $8,625 per month in refill cost to maintain a tank with 75,000scf of hydrogen gas near Aguirre. Additionally, it took three to four days for delivery. Hence, the lack of hydrogen supply forced the turbine generators to shut down and eventually disrupted Puerto Rico's critical electricity supply.
Safety is the major concern with stored hydrogen as the explosion of a standard pressurized tank holding 75,000scf of hydrogen gas would be equivalent to 5,585lbs of TNT. Hence, stringent safety standards need to be practiced to place hydrogen tanks near a power plant. Furthermore, more manpower is required for a stored hydrogen supply. For the plant, the cost incurred for storing, transporting, and refilling hydrogen tanks was estimated to be around $103,500 per year.
In a different issue the plant was seeking to find a solution was the variability of the hydrogen gas purity, pressure and dew point within the turbine-generator casings. The hydrogen-cooled generator casing purity at the plant was at around 96.9% before the installation of Nel Hydrogen's StableFlow® hydrogen gas control system. Even a minute variation in hydrogen purity can have a direct impact on a power plant's bottom line. Even a trace amount of air or carbon dioxide can significantly affect power production.
Challenges in Maintaining Hydrogen-cooled Generators at Proper Pressure and Humidity Levels
The power plant was also challenged with maintaining hydrogen-cooled generators at the proper pressure and humidity levels, which are key parameters for ascertaining the reliability and efficiency of the turbine-generator sets.
High moisture levels can cause cracking, failures, and production inefficiencies. The plant was not able to find a solution to reduce moisture levels in the generators when the hydrogen-cooled generator or stored gas supply had a high dew point. This system used a conventional Pressure Swing Adsorption drying system in conjunction with the generator to maintain a low dew point. However, the plant was not able to maintain the hydrogen in the generator casing at a steady high pressure due to the presence of the drying system.
Maintaining high gas pressure levels allows efficient removal of heat from the power generators by hydrogen. Nevertheless, the plant needed to constantly supply hydrogen in large quantities into the generator casings due to the drying system. Hence, the plant challenged with maintaining a higher, more optimal gas pressure.
Solution from Nel Hydrogen
Figure 2. Nel Hydrogen's H-Series hydrogen generator safely produces medium-pressure, high-purity hydrogen gas on-site, using only electricity and water.
To find a solution, the Aguirre Power Plant approached Nel Hydrogen, which suggested its H-Series hydrogen generator (Figure 2) as the solution. Now, the plant’s two 450 MW power generators get highly thermal conductive gas supply from a H-Series hydrogen generator. The fully integrated, packaged electrolysis system utilizes deionized water and electricity to generate high-purity hydrogen at 200psig. The plant also deployed a pair of Nel Hydrogen StableFlow hydrogen control systems (Figure 3) to maintain pressure and humidity on each generator. Puerto Rico-based AMC Engineering was hired by Nel Hydrogen to install and maintain the technology.
Figure 3. StableFlow hydrogen control systems manage hydrogen gas pressure while controlling dew point and purity.
Advantages of Nel Hydrogen’s Technology
Installation completed at the Aguirre Power Plant in May 2010, and the facility immediately realized the initial benefits of using an on-site hydrogen generator in place of its gas tanks. The installation eliminated the use of highly explosive hydrogen storage tanks and associated safety risks. The hydrogen generator supplies gas at a purity of 99.9995%.
The ultra-high purity supply of the S Series Hydrogen generators in conjunction with the gas control of the StableFlow system has continuously maintained hydrogen purity above 99% within the generator casings. Higher purity also leads to more thermal conductivity, thereby enabling more efficient use of hydrogen by the generators to produce electricity economically. Moreover, Nel Hydrogen’s technology eliminated the problematic drying system, thus allowing the system to automatically monitor and control dew point and to maintain a constant pressure of 60psi, which is the appropriate level for the hydrogen-cooled, electric power plant. This capability not only improves fuel efficiency but also optimizes generator capacity.
Instead of procuring 75,000 scf of hydrogen in tanks each month, the Aguirre Power Plant now works on the deionized water and electricity needed for the on-site hydrogen generator to produce 64 scf of hydrogen gas per hour. This allowed the plant to reduce its hydrogen budget to $15,950 per year, thus saving around $87,500 when compared to stored hydrogen.
Operating efficiency is not included in this figure. The ability to achieve higher purity and improved gas pressure and humidity control enabled the plant to save more than $2.3 million each year through reduced operational costs and increased electrical output. Improved gas purity helped the facility to produce over 5715MW/h of additional electricity per year.
This information has been sourced, reviewed and adapted from materials provided by Nel Hydrogen.
For more information on this source, please visit Nel Hydrogen.