Last week I was on the phone with Emerson’s Bob Sabin, a consulting engineer on the Industrial Energy Solutions team. You may recall Bob from some earlier energy efficiency-related posts. As I’m prone to do this time year after our annual Emerson Exchange meeting, I asked Bob if he did an Emerson Exchange presentation. He did in fact present, A Structured Optimization Plan for Leveraging Control Technology to Reduce Energy Costs and Improve Overall Plant/Mill Profitability.
Bob discussed the increasing focus on energy due to its cost and increasing emissions regulatory climate across the globe. It’s a case where greater energy efficiency is both the “green” thing to do by reducing emissions and it lowers operational costs by reducing one of the largest controllable costs. Energy usage improvement is an aspect of overall production optimization and savings go directly to the bottom line.
Bob cited an ARC Advisory Group study, Best Practices in Energy Management, which categorizes leaders, competitors, and followers in the reduction of energy usage. Half of the leaders reduced energy consumption by 10-15% each year, while over half the followers made no progress or did not know if they had made any progress.
He outlined a typical site energy-flow perspective, beginning with the sources of energy: purchased steam, purchased fuel, raw materials consumed as fuel, and purchased power. The fuel and raw material fuel are converted to steam and electrical power and consumed by the process in steam and electric drives, process heating and cooling, fired equipment such as fired heaters and dehydration units, and direct-fueled equipment and processes. The site may also export steam, fuel and power. Bob and the consulting team work with process manufacturers to assess these areas for ways to minimize (energy inputs), improve efficiency, optimize, and maximize (energy outputs).
Bob described the energy improvement process that begins with survey and measurement, followed by actions to fix field devices and loops, followed by equipment repair, followed by unit process optimization, followed by site coordination to drive the entire operation to the best cost point within constraints. Although the process is never ending, the savings are cumulative with each pass through the improvement cycle.
In the survey and measurement phase where measurements don’t currently exist, Bob recommends considering wireless devices to monitor steam flows, condensate returns, water and warm water usage, air flows, and air pressures. Wireless measurements can be implemented at a fraction of the cost of traditional wired devices. The survey and measurement phase is where benchmarks are established to monitor performance over time and compare current operations with known industry standards to establish the economic case to justify investment.
Many plants have opportunities to fix leaks, maintain steam traps and improve insulation on their steam, air, and water systems. Other areas to fix the basics include measurement device calibration and final control element inspection for linearity and repeatability. These loops are often in manual when the devices are not performing correctly. Variable frequency drives for fans, pumps, and other cyclical load devices can be more efficient than processes with recirculation loops and throttled flow.
Once these basics are addressed in a bottom up approach and the process is returned to automatic control, units can be optimized. The highest benefit is typically only sustainable if a holistic approach is taken starting with the basics. Bob recommends a “single knob” strategy where a single operator input establishes the process rate. It incorporates equipment and process constraints, coordinated rate/load changes, and bumpless, balanceless manual/auto transfer. The regulatory control can then be enhanced with advanced process control that incorporates process specific techniques and expertise. To gain the desired improvements in energy efficiency, the design targets the process controls to be in automatic mode more than 95% of the time.
Bob gives examples of simple utility operations with and without multiple fuel sources to more complex operations. No matter the complexity, the road to lower emissions and lower energy usage begins by measuring it, fixing it from the bottom up, getting on automatic control, incorporating process expertise into the control strategies, and layering models for area/site optimization. It’s also the way to move profitably from follower to leader.