Identifying Components then Optimizing Industrial Energy Consumption

When optimizing operating costs at a production facility, the bias is toward that which can be measured. For example, the cost of chemicals additives for a process is something easily measured based upon the amount consumed. For components such as the energy to produce steam, the costs may not be so clear.

Emerson's Barbara Hamilton


Emerson’s Barbara Hamilton shared a couple of stories with me about how cost optimizations changed once unknown costs could be determined.

The first example from a pulp mill, was where consistent bleaching of the pulp stock was accomplished by keeping the inlet temperature to the oxygen delignification tower constant. Oxygen was the bleaching chemical in this case.

Barbara noted that the temperature operating target is determined by the process designer, but small fluctuations in setpoint are up to the operators’ discretion. Setting the temperature up a few degrees can save bleaching chemical and setting it down a few degrees can save steam.

The Pulp Mill Operation Manager knows exactly how much the bleaching chemicals cost, but the impact of steam is not as “real”. Even if there are internal charges from the Powerhouse, they are typically done monthly and do not address incremental costs. The impact of operating temporarily away from the design inlet temperature is not readily apparent.

Energy-AdvisorFor this project, Barb and the mill staff implemented the Energy Advisor software, a Real-Time Energy Management Information System (EMIS) application that helps bring visibility to where and how energy is being consumed. This gave the mill staff the ability to measure the cost of steam production and usage and the tradeoff between bleaching chemicals and steam became apparent in real time.

It turned out that changing the temperature by even 2°C could impact energy costs by $60/hour when the incremental steam is coming from firing natural gas. The savings in bleaching chemicals by increasing inlet temperature could be completely eclipsed by the cost of steam depending upon the boiler fuel being used.

The tradeoff between oxygen consumed and steam used could now provide better decisions for the operations staff to optimized costs.

The second example Barbara shared was at a Kraft pulping facility. As any industrial powerhouse manager will tell you, not all boilers are created equal. But even when their efficiencies are known, operating procedures do not always result in the most optimum mix of fuels across the available boilers.

"Pulp mill 2" by Langbein Rise (talk) - I created this work entirely by myself.. Licensed under Public Domain via Wikipedia.

Pulp mill 2” by Langbein Rise (talk) – I created this work entirely by myself.. Licensed under Public Domain via Wikipedia.

For this process, the recovery boiler is used to process “black liquor” to recover the pulping chemicals and producing steam as a byproduct. Most pulping facilities also have a biomass boiler and it is not unusual to operate for extended periods of time without having to fire auxiliary fuels such as natural gas or oil.

Although it is generally known that recovery boilers are more efficient than biomass boilers, the operating procedures for firing the auxiliary fuel may not reflect this knowledge.

Working with the mill engineering team, Barbara showed how the Energy Advisor helped to better understand the cost of firing natural gas on the biomass boiler instead of the recovery boiler. The process engineer found that the gain factor on the recovery boiler was twice that of the biomass boiler. Energy Advisor predicted twice as much steam from the same amount of natural gas when that gas was fired in the recovery boiler.

Although there are operational reasons to fire natural gas in the biomass boiler, the mill team reworked their standard operating procedures (SOPs) to favor use of natural gas in the more efficient unit which as a result, led to immediate savings.

You can connect and interact with other industrial energy and pulp & paper experts in the Industrial Energy and Pulp and Paper groups in the Emerson Exchange 365 community.

One comment so far

  1. Running fans at excess speed, failed steam traps, fouling, inefficient combustion, pipe leaks, poor insulation on steam and condensate lines, relief valve leaks, tank leaks, unused equipment not turned off, valve leaks, and valves left open are some of the other reasons why plants are consuming more energy than they should. Poor combustion control, especially when fuel heat content changes, wastes energy by causing excessive stack losses. Leaking compressed air systems and valves left open, when not producing, waste the electricity that was consumed to compress the air. Leaking steam systems waste the fuel that was consumed to generate the steam. Pumps and fans left on, when not producing, waste electricity. Water leaking and condensate not recovered waste the water itself plus the chemicals and energy required to treat it.

    Most plants today only measure the energy streams in a single point at the source; where water, gas, and electricity enter the plant, from the air compressors, from the steam boiler, and from the utilities plant etc. Therefore there is no visibility if there are leaks in an area somewhere in the plant, if consumption is higher than normal in some plant unit, or if some equipment is running when not needed. By only looking at overall plant energy consumption, problems cannot be pinpointed so there is little or nothing that can be done to improve and sustain. Thus energy managers at most sites do not have the information they need in order to drive an energy management practices according to ISO 50001 to reduce reduction in energy consumption and losses. Whatever little data is available from the control system is infrequently put into spreadsheets manually.

    Energy management is not just about electricity. There are many energy streams flowing through a plant and all have to be accounted for in order to get a complete picture. By modernizing with additional flowmeters and wireless electric power meters at the plant area, unit, and equipment levels together with an Energy Management Information System (EMIS) plants get the ability to manage consumption and loss of energy around the plant with much finer granularity.

    Energy streams are measured for each plant area and each unit as well as for equipment with high consumption. There are five principal energy streams in plants: Water, Air, Gas, Electricity, and Steam (W.A.G.E.S), plus some others such as H2, N2, and CO2 depending on the type of plant. For air and other gases the pressure is also measured. Some of the required measurements may be available from the DCS. The missing measurements must be added. A large number of transmitters have to be deployed plant-wide metering to enable data-driven energy management. Note that these additional measurements feed directly into the historian and EMIS software; they need not go through the control system. Essential plant systems such as the water system, compressed air system, fuel gas system, electrical system, and steam system are all fully monitored. Flow readings can also be used for water balancing and other energy balances, that is, matching total energy production precisely against areas of consumption. Orifice plate or Annubar slip between existing flanges or, if flow cannot be interrupted for installation, clamp-on ultrasonic flowmeters with WirelessHART adapters are used.

    See further explanation in this article:

    Instrumental to Success
    http://www.ceasiamag.com/article/instrumental-to-success/11137

    Measurement alone doesn’t reduce energy consumption, but measurement enables excess consumption to be detected and investigated such that action can be taken. Since the flow of energy around the plant is measured with finer granularity, the energy manager gets the ability to detect and pinpoint overconsumption and leaks to a particular plant area, unit, or even an individual piece of equipment and investigate why. This in turn allows plants to uncover leaks, combustion inefficiencies, and equipment running when not necessary etc. By settling these issues sooner, plant can improve and sustain energy affiance to further reduce their energy costs. Here are two more relevant articles:

    Beyond the Control Room
    http://www.ceasiamag.com/article/beyond-the-control-room/10658

    Second Layer of Automation
    http://www.ceasiamag.com/article/second-layer-of-automation/10354

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