Information systems provide the key to energy savings in process environments
11/12/2013 Rockwell Automation
With ever increasing energy prices, energy efficiency is a hot topic. Many process applications are heavy energy users, but identifying where to make improvements can be challenging, especially for large systems with complex interactions between different pieces of equipment.On the basis that you can't control what you can't measure, monitoring is an obvious place to start looking for efficiency improvements. There will be exceptions to this where the wasted energy is very obvious and so quick payback calculations can be done for a specific item without having to set up a site-wide monitoring system, but even where this is possible, without monitoring it may be difficult to prove the savings have actually been made. In most cases, to optimise efficiency it is important to start measuring how energy use relates to a unit of production rather than just having a monthly electricity or gas bill for a whole production facility. Developing a monitoring system will typically involve installing additional meters for gas, electricity and any other power supplies, and using a communications network to pull the information into an energy monitoring software package. Because energy is used throughout the plant, ideally a common plantwide control system and network infrastructure would be used to gain easy access to all the data that is required.
Energy monitoring systems are usually expanded to cover all utilities on the site; water, air, gas, electricity and steam usage (often termed WAGES). For companies with multiple sites in the UK or worldwide it may be beneficial to install the same system in all sites so that comparisons can easily be made across multiple locations. This allows for the identification and replication of observed 'best practice' models. A good monitoring system will also alert you to potential maintenance issues such as heat exchangers failing or boiler or pump maintenance requirements if energy usage for a given production rate changes over a period of time.
Cutting energy costs can be straightforward and reap quick savings. Many process systems, for example, still use fixed speed motors for fans and pumps with dampers / throttles or no control of flow rates. These are often candidates for using variable frequency drives to improve efficiency. For example, a cement plant that traditionally used damper control systems with fixed speed motors had fans at the plant always running at full capacity - even when the facility wasn't producing product. Using variable frequency drives, energy consumption in the kilns was significantly reduced, saving over £75,000 per year.
When looking at energy savings it is possible to look at individual pieces of equipment such as large motors or boilers and make improvements on a case by case basis, but most process plants have multiple interacting processes where making changes to one part of the system will have an effect on other parts of the process.
A glass manufacturer which was able to benefit from improved information systems historically used fixed speed motors for cooling and recirculation fans. By replacing these with variable speed drives an energy saving of over 50% was made.
Replacing three fans that ran at 1800 rpm with two at 1500 rpm and one at 1350 rpm reduced the power usage from 56kW to 21kW. Careful process monitoring was required to ensure that product quality was not affected. An unexpected benefit was that reducing fan speeds also reduced the gas consumption used in the oven which highlights the importance of looking at the complete system as well as individual components. In this case the unexpected impact of the changes on the system was positive, but care needs to be taken to ensure that savings in one area don't result in additional energy being expended in another area.
To minimise capital expenditure, it is beneficial if improvements can be made by changing the way a plant is controlled rather than physically changing the plant equipment. Model Predictive Control (MPC) has the capability of looking at a large number of variables in a process plant and optimising energy usage in real-time. The MPC software can calculate the control movements required to optimise energy usage and counteract changes in raw materials or external influences such as temperature or humidity changes. In fact, in our experience, real benefits can be achieved by applying Model Predictive Control for process optimisation, some customers that have benefited include:
-€¢ A milk powder producer which increased production by 5-15% and reduced energy usage by 5-12%
-€¢ A bioethanol plant, which reduced distillation energy consumption by 5-15%
-€¢ A cement manufacturer that increased production by 10% and reduced energy and operating costs by 5%
Another area to examine is whether the physical process plant has been designed to optimise energy efficiency. Many process applications include energy usage for heating and power generation and waste energy flows out of the process. There may be opportunities to redesign the process to maximise the use of heat generated by different areas of the plant and reuse it in other parts of the process. This will involve capital expenditure but could be cost effective if the original plant design didn't optimise energy efficiency.
Companies looking at energy that has historically been wasted to see if it can be re-used in the process are reaping the benefits of reduced energy bills while also significantly reducing the carbon footprint of their process at the same time.
One example of this is on an island with a small local population. With expensive energy due to its remote location, efficiency is of primary importance to the whole community. In order to reduce consumption of energy, a school and a hospital are now heated using an automated heat reclamation system from the nearby power station. Heat that would previously have been lost from the processes at the power station is recycled and automatically managed to provide climate control for each of the public buildings at a fraction of the cost of buying energy to achieve the same effect, and the carbon footprints of both the power station and the public buildings are reduced significantly. The project had previously been studied and shelved because of problems of transferring heat one kilometre from the power plant to the buildings. An innovative solution was developed using thermal oil for heat transfer rather than traditional steam or water systems to make the project cost effective.
There are a number of well proven techniques available to understand and improve energy efficiency. With ever increasing energy prices it is more important than ever to take a look at energy usage and implement energy saving projects. As energy prices rise and look set to rise even further in the future, the return on investment for improving your process control systems becomes shorter and shorter. Add to this the stringent compliance issues concerning carbon emissions and the arguments for improving energy efficiency is a strong one.
For more information, please contact:
Rockwell Automation Ltd
UK Marketing Communications Specialist
Pitfield,
Kiln Farm
Milton Keynes
K11 3DR
Tel: 0870 242 5004
Fax: 01908 839696
Email: ukmarketing@ra.rockwell.com
Web: www.rockwell.com
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