To have a chance at being efficient, a boiler must
first be adequately loaded. This is a system issue.
Services (sometimes called “utilities”) in manufacturing plants are typically a large contributor to site energy consumption. With these services, an energy carrier such as a fossil fuel or electricity is used to transfer energy into a fluid, which is then distributed to point of use.
Some examples of common services are compressed air, steam, chilled water, thermic oil and refrigerants. Of course, the supply of electrical power may itself be considered a service.
In general, manufacturers tend to focus more on core manufacturing processes than on services, and since often the services section of a manufacturing site is managed by someone other than the managers responsible for production processes, there is poor integration between services and manufacturing when it comes to energy efficiency. The result can be a piecemeal, component-level approach to energy efficiency, when what is required is a systems approach. I started this post by saying that services tend to be large users, but we need to take a step back to appreciate that while the energy input is to the service, the drivers of that energy use lie in various plant areas, and even include environmental factors. When resource efficiency practitioners talk about “systems” with respect to services, generally we mean the generation, distribution and user side of the service infrastructure, considered as an integrated whole. In the case of some services, there is an additional system element, that of recovery (e.g. returning condensate, thermic oil or refrigerant vapour).
Let’s consider for a moment why a systems approach is important. The first point to note is that by considering an individual element of a system in isolation, one can make small improvements but miss the far larger opportunities available. Hence there could be focus on boiler efficiency which could reduce steam system costs by 5%, when all the while an opportunity exists to reduce the quantity of steam consumed, potentially reducing system costs by 25%.
A second problem with taking a component-level approach would be that in attempting to save energy, there could be unintended consequences which lead to a net decline in performance, either in energy use or in some other operational area. A simple example would be to reduce the fan speed on a refrigerant condenser in order to reduce the energy consumed by the fan motors, but to inadvertently increase the energy consumption of the vapour compressors, thereby increasing system-level refrigeration energy consumption.
A third and vital reason to take a systems approach to services optimisation is that the individual elements of the system interact with each other, and when implementing a basket of solutions comprising projects in each individual area, the implementation of each solution will influence the impact and viability of the others. A heat recovery project for a compressed air system will reduce in attractiveness should the amount of air required be significantly reduced, for example. The point here is that the benefit of implementing a portfolio of solutions for a given system will generally always be less than the sum of the individual solutions. This implies that it is useful to have a view of the full portfolio of planned solutions before proceeding with implementation, and while this is not universally true (e.g. one should not hesitate to fix air or steam leaks), it is important when considering capital-intensive options.
Reducing the pulse frequency for this bag filter
would reduce compressed air consumption. This
would reduce the loading of the air compressors.
Almost without exception, the approach to energy efficiency I see in most manufacturing plants as regards services is as follows:
i. Tinkering with the distribution network e.g. insulating distribution pipelines, fixing leaks and the like;
ii. Investing heavily in generation e.g. an “efficient” new air compressor, replacement of slide valve control with VSD control for refrigeration compressors etc.
There is no harm in dealing with obvious inefficiencies in distribution. The costs for implementation in this area tend to be low. At very large facilities, the savings can be significant. In general, however, projects involving the distribution network tend to yield only modest savings, and if this is all you are going to do, don’t expect breakthroughs on the bottom line. There are some distribution problems that do however require system-level considerations – an example would be a project to increase the size of air distribution pipelines to reduce pressure drop, which may become unnecessary should air use be significantly reduced.
The focus on generation I referred to above is in part due to the fact that there is a relentless focus on technological development in this area by OEM’s. Shiny new machines are attractive, and tend to come with assurances from suppliers with respect to increased levels of efficiency. Exercise extreme caution however. Many technologies only operate optimally when used in the correct context. Establishing this context requires a consideration of the system. As a simple example, a VSD air compressor as a replacement for a fully-loaded fixed-speed machine will not yield savings. A second reason that organisations tend to focus on the generation side of the system is the common misconception that efficiency needs to be “bought”, and that older installations cannot operate efficiently without investment. Since the generation side of the system is where capital tends to be concentrated, the tendency is to spend in this area. The reality is however that there are any number of no-cost and low-cost options that may be employed to drive energy efficiency.
The recovery aspect of some systems offers significant opportunities. In steam systems, condensate and flash steam recovery options can offer large savings at relatively low capital cost. Their viability is however impacted on by system-level considerations. A change in the steam pressure supplied to a user could significantly reduce the amount of flash steam produced, for example.
Given the above, you have most likely figured out by now that the place to start when optimising services is on the user end of the system. This means finding ways to reduce the amount of service fluid required. This comes with a lot of good news. In general, user-side opportunities abound. And in many cases, a common-sense approach can yield large benefits. Close those freezer doors. Insulate those process vessels. Recover energy from the leaving process stream. Automate the operation of that system so that switching off equipment is not dependent on someone remembering to do so. It may also be necessary to challenge paradigms in your business to reap these benefits. Does that process really need to operate at that temperature? Do we really need to wash this pipeline with hot water after each and every batch? Does the air pressure to that nozzle really have to be 8 barg. or can we get away with 5 barg?
When you take the time out to do this, you could be surprised by the quantum of the savings possible. That is one big reason to start here. The second is that there will be knock-on effects for the rest of the system. You may now only require two vapour compressors in your refrigeration plant room instead of three. The back-pressure turbine you thought was viable is now no longer so, since the amount of steam used has been significantly reduced. Your fully-utilised chiller plant is now a candidate for the implementation of a VSD compressor, since you now operate at part-load conditions for much of the time. You thought that you needed a VSD air compressor, but can now switch one of your compressors off. Had you made investments in generation, distribution and recovery before optimising your users, you could have ended up with a sub-optimal system.
Copyright © 2016, Craig van Wyk, all rights reserved