Gas engines cure power supply reliability problems at Puerto Rico hospitals

Above: Hospital Menonita De Caguas and the new cogeneration plant

When disaster strikes it is crucial that the emergency infrastructure is ready to play its part, prime among critical facilities being hospitals.

As we enter the Caribbean hurricane season, the 44 million inhabitants keep a constant ear to the Caribbean Hurricane Network for advanced warning on the path of the series of hurricanes that blight the region each year. There are 26 Caribbean nations, but the archipelago encompasses more than 7000 individual islands in an area of approximately one million square miles. The region is prone to hurricanes, with the season lasting from June to the end of November, and up to eleven hurricanes forming each year.

One such Caribbean island is Puerto Rico. With its problematic power grid and annual hurricane season, it’s crucial to ensure power supply to hospitals. To achieve this, Siemens Energy is supplying distributed generation solutions with its propane-powered gas engines. When Hurricane Maria hit Puerto Rico in September 2017, it was the worst natural disaster in recorded history to affect those islands. It was also the deadliest Atlantic hurricane since Hurricane Mitch in 1998. Sustained winds of 155 mph swept across the Caribbean island, uprooting trees, destroying infrastructure such as weather stations and mobile phone towers, and ripping roofs off homes.

Almost 3000 inhabitants lost their lives in the storm and its aftermath, but aside from the human cost, there was a further price to pay in the devastation the storm inflicted on the local infrastructure. Electricity was cut off to the entire island, and access to clean water and food became limited for most, plunging the island’s 3.4 million inhabitants into a desperate humanitarian crisis.

It took almost a year to fully restore power and for the Puerto Rico Electric Power Authority (PREPA) to announce in August 2018 that it had finally reconnected all 1.5 million customers to the power grid, ending the largest blackout in US history and the second-largest blackout in the world. However, that stark fact does not paint the entire picture. The funding to restore the power infrastructure came through US federal disaster aid from the US Federal Emergency Management Agency (FEMA) and only covered repairs to restore infrastructure to its previous state, not a much-needed upgrade that the network desperately required.

More distributed generation

Even before the hurricane, the island’s power grid was notoriously unreliable and power cuts were a regular occurrence. However, there is light at the end of the tunnel for the long-suffering residents, with PREPA finally releasing its revised Integrated Resource Plan late last year. The 20-year plan is said to be better aligned with the territory’s goals of using sustainable, renewable energy and is a step forward for the island after its first plan received significant pushback for being too reliant on fossil fuels. One of the plan’s critical elements is the greater use of distributed generation, microgrids, energy efficiency, and demand response. The distributed generation will reduce the island’s reliance on electricity that is now brought by transmission lines over its mountainous centre.

To ensure that operations can continue in the aftermath of storms, some of the islands’ critical infrastructure facilities are employing local generation to safeguard the security of their electricity supply.

One such facility is Hospital Menonita De Caguas in Caguas, Puerto Rico. Although it will remain connected to the power grid, the hospital had a two-fold requirement from its new local energy source. The hospital wanted a system to deliver heating and cooling to the hospital but also wanted a secure electricity supply in the case of a grid outage. The solution consisted of two Siemens Energy containerised cogeneration modules based on SGE-48 SM 1800 rpm 480 V 60 Hz propane fuelled gas engines, compliant with Puerto Rico legislation. The power output is 856 kWe per engine, providing a total of 1.712 MW of electrical power.

The exhaust gases from the engines are used in a heat recovery boiler to generate steam, while the hot water from the engine main cooling circuits is fed to an absorption chiller. Thermal heat recovery together with electricity generation enables the CHP plant to achieve total efficiency above 80%.

The lean-burn and electronically carburetted SM series of gas engines provide an excellent option for power generation, cogeneration and trigeneration applications. They can be fuelled with natural gas, landfill and sewage gas, and propane LPG. Outputs range from 255 to 2065 kWb when fuelled with natural gas, landfill, or sewage gas in 50 Hz and 60 Hz configurations. When fuelled with propane or LPG, outputs are from 275 to 1067 kWb at 50 Hz and 60 Hz, respectively.

The Miller cycle series of engines is turbocharged and includes two-stage charge air cooling depending on the engine model. The auxiliary circuit allows different cooling temperatures to be used, providing best performance under any ambient conditions. The configuration of the oil cooler in the main cooling circuit is an option when the engine is intended for CHP applications.

Containerised ‘plug and play’

Among the key characteristics of this series of engines are standard interchangeable parts and very high operational availability, which are key competitive advantages.

With a dry or wet exhaust manifold configuration depending on the fuel gas type used, an emissions control option means this series is compliant with the latest US emissions standards and has reduced oil consumption. The engine series may be supplied as a standalone engine, a genset or a fully containerised unit.

The containerised ‘plug and play’ nature of the technology as well as locally available round-the-clock service capability and multiple reference units were also significant influences in selecting the SGE-48 SM for the Menonita project.

The Menonita unit operates in trigeneration mode, providing power, heat, and cooling simultaneously. The heat recovery boiler produces 1300 pounds per hour of process steam for the hospital, while recovered energy from the engine water jacket system fed to the absorption chiller generates cold water for the hospital at 5°C.

The Hospital Menonita project was delivered by local EPC company, Teksol, whose services include consulting, project management, staffing, provision of turn-key CHP systems based on Siemens Energy engines, automation, instrumentation and control, and systems integration.

This was not the first instance that Siemens Energy had supplied a distributed generation asset in Puerto Rico. After hurricane Maria, the eastern municipality of Yabucoa would be without power for eight months, but one of the companies located there, Olein Refinery and Lubricants, was operational just five days after the storm hit. Olein, which manufactures automotive fluids, was not reliant on the local grid, thanks to an on-site combined heat and power plant installed by Teksol Integration Group and powered by two propane-fuelled Siemens Energy SGE-24 SM gas engines.

In this cogeneration system, heat from the gas engine exhausts powers a chiller that produces cold water to cool machines throughout the facility.

Why gas fuel is optimal

Gas fuels, natural gas and propane, have become the preferred option for cost and environmental reasons. Another crucial factor in favour of gas fuels is the security of supply. There was extensive damage to the highway infrastructure after hurricane Maria, so backup power units at emergency units in hospitals and industry ran out of diesel. In contrast, facilities that operated on gas fuels had stocks on hand.

At Hospital Menonita De Caguas, Empire Gas recently completed the process of installing propane gas supply to the new cogeneration complex. This project is part of our contribution to achieving the highest level of efficiency in the hospital facilities that adopt it.

For Hospital Menonita de Caguas, the project is more ambitious because, in addition to becoming self-sufficient in electrical energy, the hospital complex will have a modern potable water treatment and storage plant and an oxygen generation plant, both capable of supplying all the hospital’s needs. The water treatment and storage plant were also built by Teksol.

Such has been the success of Siemens Energy’s collaboration with Teksol on the Hospital Menonita project, the plan is to replicate it across four more hospitals on the island, which is good news for Puerto Rico’s inhabitants.

Authors: Gabriel Craig is Latam regional sales director at Siemens Energy Engines, Buenos Aires, Argentina (gabriel.craig@siemens-energy.com); and Xabier Beroiz Oliden is portfolio consulting professional at Siemens Energy Engines, Zumaia, Spain (xabier.beroiz@siemens-energy.com)