Revamping Geothermal: The Mori geothermal start-up

The gradual, global movement from traditional to alternative energy might be a more recent endeavor, as we seek less harmful and more energy efficient ways to power our planet. But, geothermal energy (or, the heat from the earth) has been used for centuries. From bathing and cooking since the Paleolithic times, to heating since ancient the Roman times, hot springs have provided heat and fresh, warm water to humans for ages.

In more recent times, the earth’s springs have been used to generate not only heat, but also power and electricity, and can often be found in even the most remote regions of the world. A small town in the Hokkaido prefecture of Japan, Mori, is just one example. Mori is home to a geothermal power plant that has been generating electricity for the inhabitants of Hokkaido for more than 30 years now.

This plant was originally designed to produce 50 megawatts (MW) of electricity for the grid but, as with anything, changes over time have impacted its efficiency and workflow. In this case, specific changes in the geothermal resource—which can include how much energy is in the steam, the quantity of steam available, or the amount of non-condensable gas present in the steam—have gradually reduced the plant’s output to about 15 MW. At the Mori plant, the resource is brine, which is flashed or expanded into steam in order to drive the turbine.

Not surprisingly, the town and company contractor identified the Mori plant as one that was in desperate need of improved efficiency. Fortunately, a team of engineers could provide just that.

Plant upgrades
Any system inefficiencies can noticeably impact the power of a geothermal plant, affecting the energy it can produce for the grid. This is especially true of a plant with a gas extraction system, which can account for one of the largest parasitic loads on a geothermal power plant—and was the case for the Mori plant.

With electricity capacity so low (at only 15 MW), the Mori plant owners (Hokkaido Electric) were convinced to upgrade the plant’s gas extraction system. A simple plan, perhaps, but no easy feat. The original system consisted of a turbo blower, which was driven by a steam turbine that also helped drive a generator. The plan during this upgrade was to remove the existing turbo blower, which had a gross weight of 220,000 pounds. Removal of the system required proper planning. This work took approximately two months, but was nicely timed to coincide with the plant’s bi-annual maintenance shutdown.

For this project, it was out with the old and in with the http://new. In place of the turbo blower, a new, hybrid gas removal system was designed for the Mori plant, engineered to work with its current, non-condensable gas load. In terms of efficiency, the hybrid system used much less power than the original blower. The hope was that the plant would provide closer to 18 MW of power after the upgrade.

To help with the switch, a start-up team was sent to the jobsite to monitor and check the installation of all of the equipment. During the five days this engineering team was at the plant, the pump and the entire gas extraction system were started. The turbine was balanced, while cycling through various loads, and then the whole unit was started. The generator began putting power out to the grid as intended.

In fact, the new gas extraction system responded better than originally intended. As a result, the team increased the load from the anticipated operating level of 18 MW, to over 20 MW. Even though the gas content of the steam was higher than the system was designed for, the condenser vacuum held steady and the gas removal system continued to operate flawlessly.

Final operations
The final goal of this project upgrade involved reducing and analyzing all of the data acquired at the Mori plant, and presenting it to Hokkaido Electric’s plant management. The data showed a minimum increase of 5.5 MW output over the previous system, which was even higher than what was predicted or designed for the non-condensable gas amounts—and, actually, equated to almost twice that of what was initially guaranteed for the upgrade. Even better, were the payback figures, which showed that the plant upgrades reduced the originally computed payback time for the project by almost 50%.

Before leaving the Mori plant, the engineering team provided a hands-on demonstration and instruction session for plant personnel on the proper operation and maintenance of the new gas removal system. Upgrades are of little value if the equipment isn’t run or maintained properly.

As far as geothermal plant upgrades go, however, the Mori plant proved to be a successful, well-executed project, demonstrating the ongoing benefits of an age-old energy source from the earth—the power of geothermal energy.

Gardner Denver Nash
www.gdnash.com