Environmentally friendly or efficient? Marcus Geigle reveals a control solution that covers both bases
In electric power plants based on gas turbines, a steady supply of fuel gas at a constant pressure is crucial for economical energy production. This is possible – and with unprecedented reliability – thanks to advanced capacity control of high-speed compressors upstream of the gas turbines.
The world’s first all-electric stepless capacity control system, eHydroCOM, proved its value when together with the Hoerbiger CP valve it was installed in one of Europe’s most modern gas-fired power plants at Tepláreň in Slovakia.
The industrial Slovakian town of Považská Bystrica is home to Tepláreň, which as part of the energy company Graphobal Group Energy (GGE), has supplied more than 40,000 people and hundreds of companies with electricity and district heating since 1972. In 2014, this regional provider produced 250,000MWh of power and 200,000MWh of district heat to feed networks operated by the public utility Teplo GGE.
Between 2009 and 2010, Tepláreň installed new technology to convert its power plant from coal to more sustainable natural gas in just 18 months. The result was one of Europe’s most modern gas power plants, which met EU emissions targets for 2016 well before deadline and ensures that the site is ready for the future.
The plant’s efficiency and reliability depend on a GE Gemini compressor at its core. Known as a fuel booster, this unit takes gas from the supply main at a fluctuating pressure of around 20 bar. Operating at 990rpm and with a power consumption of 600kW, the compressor provides a constant 45.6 bar discharge pressure to feed the GE gas turbine that drives the generator.
The compressor’s steady discharge pressure and low energy consumption are made possible by Hoerbiger performance-defining compressor components and services. eHydroCOM, the company’s stepless capacity control system, is combined with the new high-performance CP valve with PowerPEEK technology, plus comprehensive on-site service.
Tepláreň and Hoerbiger began working together in 2012, after the power plant had been upgraded and converted to natural gas. Initially, Tepláreň was merely searching for a service company for the compressor package it had purchased from a New Zealand supplier. Service from New Zealand was becoming expensive and cumbersome, so Tepláreň sought a partner closer to home.
In addition to technical expertise, high local availability of the service technicians was a key factor for Stanislav Bednar, Tepláreň’s technical director, and Eduard Lecko, the company’s director of production. The Hoerbiger service organisation in Slovakia met these requirements and was awarded the contract. Initially, the company carried out scheduled maintenance using the compressor manufacturer’s specified replacement parts.
After the service team had completed its first appointment, however, Bednar and Lecko inquired whether there were ways to operate the fuel booster more efficiently and also more reliably.
Since the start of continuous operation on gas, it had become increasingly apparent that the chosen compressor solution was wasting energy within the production process.
Additionally, Tepláreň was plagued by too much unexpected downtime for a wide variety of reasons. Under its contract with the public energy company SEPS, Tepláreň had to make repeated compensation payments to cover the downtime. These payments were not affordable in the long run.
Efficiency and reliability improvements
Gabriel Szlavik from Hoerbiger’s service location in Slovakia, suggested installing alternative components that would perform better than the standard products being used at the time. First, a Hoerbiger REE (Reliability, Efficiency, Environmental Soundness) audit was performed to show whether there was improvement potential in terms of compressor efficiency and reliability.
Tepláreň benefitted directly from the experiences gained with this new service Y Improvments approach, which uses standardised processes to identify potential improvements to increase efficiency, reliability, and sustainability.
With the assistance of Hoerbiger Engineering in Vienna, Austria, the weak spots were quickly established and solutions developed. To begin with, CP valves optimised for the compressor were installed, replacing the existing valves. This was the first step in what would ultimately become a considerable boost in efficiency and reliability. In a further step, lubricating oil losses were minimised by replacing the sealing elements of the piston rod with OFD wiper rings
Stepless capacity control
The primary reason for the compressor’s low energy efficiency and frequent stoppages, however, was the control system the company was using.
The compressor was running constantly at full load; if the turbine required less gas, the only way to achieve this was to recycle compressed gas through a bypass valve and back to the compressor inlet.
Also, due to the wrong configuration of the bypass and the filtration system, the recycled gas contained way too much oil, which regularly led to clogged suction valves. This process wastes a lot of energy in needless compression, since the pressure energy in the gas flowing through the bypass cannot be recovered.
Stepless capacity control is a better solution. Tepláreň was seeking to achieve energy savings of up to 20% through advanced capacity control. The company opted for the eHydroCOM all-electric stepless capacity control system. eHydroCOM requires no hydraulic lines, hydraulic power pack, or external cooling system. As a result, it has a very small footprint, making it well suited for the Tepláreň plant, where an enclosure restricts the space avail-able around the compressor.
Apart from the valve actuators themselves, eHydroCOM requires only a compact ePU (Electric Power Unit) to supply power and data, with a single cable to each actuator. The Tepláreň ePU was conveniently installed on the rear wall of the compressor enclosure.
55% energy savings
The autumn of 2014 saw a rather bumpy start adapting eHydroCOM to the conditions in the Tepláreň plant. Since then, the new stepless capacity control system has run flawlessly, achieving unexpectedly large energy savings.
Stanislav Bednar says: “We were looking for 20% energy savings, but today we’re at 55%. This means hard cash saved for us every month, which we can invest in additional process and technology improvements for our plant.”
With a smile, Bednar adds: “I have to admit that I was not very happy about the start of the process. We were told that eHydroCOM would be completely installed in one day and would then be immediately productive and virtually maintenance-free. Unfortunately there was a logistical problem, and the shipment arrived late. After unpacking the unit, it turned out that we received a configuration that did not fit. So we had to go through the whole process again. The plant was shut down during this time, and we were on the verge of some serious problems. Still, the Hoerbiger Service staff kept a cool head in this critical situation and pulled out all the stops to have the right components shipped as quickly as possible – including an additional engineer and control specialist, Dr. Peter Dolovai, the Mechatronics team leader from Research and Development. He personally completed the successful installation, and it was then that we knew we had chosen the right service company.”
Marcus Geigle is with Hoerbiger.