"The boiler upgrades are helping us make better use of ‘indigenous' waste fuels, such as blast furnace gas, BOS gas and coke-oven gas, which are byproducts of our manufacturing process," says Andrew Rees, manager of Tata Steel's upgrade project. "The improved controls are part of a comprehensive energy management project that's expected to reduce powerhouse energy consumption by 3% to 5% and help us achieve our vision of becoming energy self-sufficient."
To begin the Port Talbot upgrade, Emerson conducted a study to identify opportunities for improving powerhouse operations, and then designed and delivered the most appropriate integrated combustion-control, burner-management and energy-management solution. It included Emerson's SmartProcess Energy and SmartProcess Boiler optimization technologies, DeltaV digital automation system with model-predictive control, DeltaV SIS process safety system, Rosemount and Micro Motion measurement instruments, Fisher control valves, and Bettis and Hytork valve actuators.
In the past, the plant's boilers needed frequent attention, and had to use supplemental natural gas to compensate for varying energy content of waste fuels. Following the upgrade, operational stability was increased, and energy costs declined because more efficient use of waste fuels reduced the need for natural gas. Using more waste fuel to power the boilers instead of burning it in flares also helps reduce emissions.
Green Needs Control, Too
Naturally, after considering a few of the latest sustainability projects, it becomes clear they share a common thread with traditional process control—all are based on sensing physical properties, analyzing complex data and acting on the resulting decisions. For example, Center Ethanol Co. and its four-year-old plant in Sauget, Ill., near St. Louis, turns 19.2 million bushels of corn into 54 million gallons of ethanol, 172,000 tons of dry distiller grain and 1.5 million gallons of corn oil per year. To optimize and gain production efficiencies in its applications, Center's staff and the former Delta-T Corp. in Williamsburg, Va., installed Siemens Industry's Simatic PCS 7 process control system. The staff also built screens on PCS 7 outlining standard operating procedures for starting, stopping and shutting down equipment, and also introduced programming that instructs operators how to fix out-of-range process parameters. Faceplate and interlock screens enable operators to click on a symbol, such as a pump, drive, valve or PID loop, and quickly determine the status of the device and process interlocks. Operators also have a view of the entire plant from the control room and can drill down into process areas or devices.
"If a process goes out of parameter, an alarm alerts technicians in a central control room with four operator stations," explains Tim Kostecki, Center's operations manager. "The operators can check the equipment, or cross-check what it's saying against what the lab is telling us. This has improved temperature, pressure and many other control variables."
Center also has added programming to better control its enzyme and chemical additions, as well as front-end corn grinding and fermentation processes. "We're saving more money because we can optimize chemical additions to the process," explains Kostecki. "The new programming ensures that we start off with the right recipe for fermentation. When you control your front end and get your fermentation in a steady state, the whole plant runs more efficiently. If you're going up and down all the time—such as one fermentor is at 14% and another is at 13%—then it will swing around the distillation at the back end, so you can't get your fermentation to be the same ethanol concentration every time."
Kostecki also reports the trending capability of the plant's control system gives operators at least three months of historical data that can be loaded into an Excel spreadsheet, eliminating the need for time-consuming manual data entries.
"We use trending every day," says Kostecki. "We know if our system is running out of tank room. But rather than slowing down the plant, the guys in the control room can graphically track and manipulate tiny changes in tank levels. It also uses the trending capability to make sure dryer temperatures, pressures, flow rates and amps are at the right levels.
"When you're monitoring and logging data as part of an energy efficiency strategy, it's important to analyze power consumption data that you collect in context with other data related to that application," adds Ben Orchard, application engineer at Opto 22. "For example, if you're trying to reduce facility power consumption, you need to gather data on suspected large loads such as chillers. You then need to gather data that put that chiller load in context, such as the room temperature for rooms serviced by that chiller."
Of course, if operations can be optimized for greater sustainability in one application, then the next job is to do it at multiple sites. To monitor and alarm stack emissions, comply with legislated limits and avoid the possibility of required shutdowns, South Africa-based Eskom partnered with Bytes Systems Integration and Invensys Operations Management to optimize operations at Eskom's 13 coal-fired plants.
"Without treatment, we'd spew concentrations of 30,000 to 60,000 mg of ash per normal cubic meter (mg/Nm3) into the atmosphere," says Dr. Kristy Ross, senior consultant at Eskom. "However, by using abatement technology, such as electrostatic precipitators or fabric filter plants, more than 99% of ash is removed from the flue gas streams, providing a particulate emission concentration of usually less than 200 mg/Nm3."