Control Upgrade Increases Turbine Efficiency

Dec. 15, 2016
A paper producer adds new HMI graphics and control platform to increase uptime with its gas turbine power center in a Western European plant.

Local power generation has always been a challenge for manufacturers, as it’s usually viewed as a non-core function. But companies are now seeing the benefits in better energy efficiency and bottom-line savings. However, legacy plants need help to achieve energy efficiency targets.

Turbine technology hasn’t changed much over the years, but legacy control platforms in today’s plants can’t provide adequate redundancy, speed or visibility into process parameters to avoid unplanned downtime. A recent integration project for a large paper producer in Western Europe that uses a gas turbine to produce electricity and steam for facility and industrial processes illustrates this challenge.

A standalone, legacy control system became inefficient because of false positives with process instruments and a harder time replacing older equipment. This large paper manufacturer hoped that a new control and monitoring system could increase performance and reliability for the gas turbine setup.

“It’s hard to calculate return on investment (ROI) for such projects,” says Harry Pigler, chief operator officer at Pigler Automation, a Longmont, Colo.-based integrator tasked with the project. “It comes down to: If you don’t upgrade the control system, then it will eventually fail and cause an extended downtime due to hard-to-locate spare parts.”

The paper manufacturer decided to replace the aging turbine control system with new control hardware and software from Siemens. The new platform consisted of the PCS 7 control system with an AS 410-5H processor, along with seven I/O racks. The new control platform automatically provides default processes to correct potential parameter variations, such as a thermocouple variation from the turbine’s exhaust. Another essential feature was the ability to inform operators where and how to make manual corrections in response to certain events.

The turbine power plant has about 500 I/Os. The new standalone control system—separate from the plant’s distributed control system (DCS)—communicates with a Delphi vibration monitoring system.

A key enabler for better-informed operators was the control system’s new high-performance graphics for operators. Siemens’ Advanced Process Graphics HMI interface provides operators with displays of health and status of the turbines in a schematic representation.

“The human eye can quickly detect visual deviations in displays, such as when lines are not perfectly straight or when a circle is not perfectly symmetrical,” Pigler says. “The graphics on operators’ computer screens clearly indicate, in a well-arranged manner, if something is not quite right with the turbine.”

The object visualization is based on the data collected by the system’s connector block in the automation system, which is tied to code inside the controller. With control room HMI setup, a circular spider graph measures predefined temperature parameters assigned to exhaust emissions. During integration of the system, Pigler Automation just copied the block icon and the 18 tags used in the process. From there, the dynamic wizard assigned appropriate tags and automatically positioned them around the spider graph, saving a great deal of time. The exhaust temperatures are also displayed in a polyline graphic that moves as temperatures change. “If a spike or drop in temperature happens, the line will shoot straight up or down, respectively,” Pigler says.

Graphic types include graph charts, polyline displays and bar graphs that present multiple data points to determine if states are “good” or “in trouble.” Other operator values include vibration, shaft displacement and motor temperatures. The vibration parameters for non-drive and drive-in bearings, gearboxes and generators are shown via different polylines.

With such a large power plant, the platform controls and monitors more than 140 analog devices, with 105 being overseen via bar graphs summarizing data on several pages in the HMI. The bar graphs exhibit low and high alarms depending on whether the turbine is starting, in warm-up phase or at full load.

Bar graphs can be customized when combined with the system’s Advanced Process Library’s icon, which is important when operators and maintenance teams need to adjust graphics as they look for more efficiencies. “With some training, the operation team can change graphic layout or add information to the screen,” Pigler says. “The HMI changes are usually the easy part.”

Bar graphs can also be combined into frames, with these representing analog monitoring blocks or PID controller blocks. For example, if an operator clicks on a frame, a faceplate is opened that belongs to that analog measurement or PID controller.

These bar graphs come in standard gray outline, the preferred strategy per ISA 101, but the paper company wanted to clearly see if alarm limits were being approached. So Pigler customized the change colors—red, yellow or blue—as the process value passed the setpoints.

“From our point of view, the graphics makes it easy to shine as an integrator because of the outstanding advanced functionality it provides,” Pigler says. “The customer likes it because of the compact, easy-to-grasp visualization.”

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