PDCA methodology reduces startup losses

2015 CCJ Best Practices Awards: Best of the Best

Jordan, a rapidly growing country lacking indigenous energy resources, relies heavily on imports to meet its growing demand. Natural gas is brought in from Egypt via pipeline, fuel oil from Saudi Arabia via ship.

AES Jordan’s Amman East Power Plant, a 420-MW, 2 × 1 combined cycle located in Al Manakher and designed for base-load service on gas, is now starting daily and operating on fuel oil because gas is not available. Plant Manager Meftaur Rahman said that when the plant burned gas it averaged about 10 starts per year; today, operating on oil, it starts about 240 times annually.

Startup losses are significant on oil and the Amman East team studied how to reduce them, beginning with a review of current procedures and manuals; also, by benchmarking their operation against plants in Jordan as well as in other Middle Eastern and European countries.  

According to AES Jordan’s Power Purchase Agreement (PPA), the plant is not limited on the number of annual starts. This affords an opportunity to improve performance beyond typical market metrics. Bear in mind that frequent starts and stops create many challenges in plant performance—for example, heat rate, water consumption, and noise for the local community.

Some challenges were observed during the frequent startups on oil, including these:

      • Lower efficiency (higher heat rate) at low load, increasing fuel consumption.

      • Increased water use attributed to high-pressure steam loss from the startup vent.

      • Although the business meets World Bank guidelines regarding startup noise, the frequent starts disturb the local community—especially during the early morning hours.

The plant’s goals were the following:

      • Reduce heat-rate losses during startup to save $70,000 to $100,000 annually.

      • Reduce water consumption by 1300 to 2600 gal per start.

      • Determine how to reduce noise during startup by 2 to 7 decibels (dB).

      • Reduce startup time by 20%.

      • Develop a more cost-effective startup procedure for operations personnel.

Solution. The team used “Plan, Do, Check, and Act” (PDCA) methodology and related tools, such as Ishikawa and brainstorming sessions, to meet the stated goals. The 5W2H technique was subsequently used to support the analysis with specific targets, because of the various issues raised.

The PDCA method then was applied to test proposed solutions, ensuring their impact and sustainability. Plant management engaged the operations staff to analyze the situation and find an innovative solution. The results illustrated teamwork and process. After identifying the variables impacting startup performance, the team used a cause-and-effect diagram to find the most significant factors affecting the startup process (Fig 1).

Amman East BOB Fig 1

These four root causes of startup performance loss were identified:

      • Gas-turbine load ramp rate was lower than recommended in the operations manual, increasing the time required to start up and the time required to raise steam pressure and temperature to the 588-psig/932F required for steam from both HRSGs to merge and flow to the turbine.

      • Operations personnel were opening the sky vent wide (45% of full flow) late in the startup process, thereby releasing to atmosphere a large quantity of high-pressure steam. This procedure contributed to high water consumption and excessive noise.

      • Operations staff knowledge and awareness of heat-rate losses during startup was shallow and needed improvement.

      • Distributed control system (DCS) monitors did not show ramp rates for pressure, temperature, and load, nor indicate startup duration.

Amman East BOB Fig 2, 3

Solutions implemented included the following:

      • Increase GT load ramp rate from 0.27 to 0.38 MW/min by increasing the ramp-rate set point. This helps to reduce the startup time by 20 min (Figs 2, 3).

      • Open the sky vent to 18% of rated flow when the GT is synchronized; then follow the curve in Fig 4 until pressure and temperature reach the 588-psig/932F merge values noted earlier.

      • Increase operator awareness regarding startup losses and ways to control them by conducting both training sessions and day-after discussion of the previous day’s startup.

      • Added ramp rates in the control screen for pressure, temperature, and load.

Amman East BOB Fig 4, 5

Results. With the development of, and efficient startup procedures for, cycling on both oil and gas, staff has become more knowledgeable and efficient regarding the startup process and loss minimization. Implementation of these solutions successfully saves around $100,000 annually and reduces startup duration by 20%. Also, the solutions can be replicated across the eight combined-cycle plants in Jordan.

Amman East BOB Fig 6

From an environmental perspective, Amman East now saves around 650,000 gal/yr of water, ensuring the plant will not exceed permitted consumption. Noise pollution is mitigated both by optimizing opening of the startup vent, which reduces noise by 5 dB, and collaborating with the off-taker to avoid starting the plant during late night and early morning hours. Plus, plant personnel decided to install a vent silencer at the next outage. The plants success in controlling startup losses is profiled in Fig 6.

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