The high energy costs continue to present a major obstacle hindering country’s manufacturing performance. A survey highlighted the cost of energy as a major concern for manufacturers, with many identifying it a key factor impacting on their profitability and competitiveness. On sites where steam and hot water is used, significant cost savings can often be found in the boiler house and steam distribution system. Here are ten top tips that can help optimize steam boiler efficiency.
1. Measure
However sophisticated your planned energy management strategy might be, it starts with one essential realisation – you can’t manage what you can’t measure. The steam and hot water that most companies use to provide process and space heating have to be monitored closely.
This will allow companies to see which parts of their operation are incurring the biggest energy costs. Being able to pinpoint exactly who is using what enables managers to adopt far more sophisticated accounting procedures and encourages operators to take more responsibility for energy usage in their own areas. It also helps to spot issues such as leaks or malfunctioning equipment, which could be haemorrhaging cash if the problem is allowed to continue until the next maintenance survey.
Instrumentation presents the vital front line in any drive to become more energy efficient. When used to its full potential, an instrument and / or analyser can provide you with a full indication of what’s happening within your process, enabling you to make informed decisions about potential improvements.
2. Make sure you’re generating what you need
Measurements should not only be taken at the boiler but also around the steam distribution system in order to ensure that supply is properly matched to demand. This may be particularly relevant where equipment has been replaced or a control system has been upgraded, resulting in reduced steam consumption at the point of use.
Making sure that the right quantity of steam is going where it is needed will ensure you’re not wasting steam heating up your factory instead of your process. You should also check that the boiler duty is at optimum efficiency. For example, don’t use two boilers operating at 30 percent output if you can run one at 60 – 70 percent output.
3. Keep an eye on what you’re using
Steam metering throughout the entire distribution system is crucial for good energy management. Proper metering allows you to see exactly what’s going on. For example, meters can track the consumption of individual user processes across a site. This enables energy managers to encourage efficiency by introducing separate billing, or target energy saving measures where they will have the most effect.
Trend information also enables operators to spot malfunctioning equipment or other problems as they develop. Videographic data recorders offer an ideal tool for collecting and retrieving data as part of an energy management programme. These devices enable vast quantities of data to be collected, which can then be readily interrogated to help identify specific trends and events that can be used to help optimise efficiency.
4. Use the right sort of flowmeter
Accurate metering is the key. Operators need to know the mass of steam moving around the plant, since this equates to the energy flow. Traditional differential pressure meters such as orifice plates require peripheral paraphernalia including differential pressure transmitters and a flow computer to produce mass readings for steam, all of which adds up to a high-maintenance headache.
In contrast, swirl meters have lower maintenance requirements and deliver greater accuracy, especially in applications where the steam flow varies over a significant range. Rather than an accuracy of two percent of the upper flow range, which is the best an orifice plate can provide, swirl meters offer better than one percent accuracy over the entire flow range. Furthermore, the turndown is up to five times greater than that of an orifice plate. Swirl meters rely on static veins at the entrance to the meter to force the fluid into rotation. The meter then measures the frequency of a helical secondary rotation that automatically develops within this pattern.
The frequency of the secondary rotation is directly proportional to the volumetric flowrate of the fluid, without any need to compensate for changes in pressure, temperature or density.
A major advantage of swirl meters is that only the temperature of the steam is needed to calculate the mass flow, eliminating the cost, space and maintenance associated with additional equipment. Where companies are looking to retrofit meters on existing steam systems, swirl meters offer the added advantage of being able to fit almost anywhere. Most flow meters need to receive undisturbed flow to deliver accurate results, which means they need to be positioned a good distance downstream from pipe bends, valves or other components that might interfere with the readings. Swirl meters overcome this, with just three pipe diameters upstream and two diameters downstream needed in most applications.
5. Keep an eye on your boiler chemistry
Heat transfer surfaces must be clean in order to conduct heat efficiently, but fouling can also be a problem on the ‘wet’ side of the boiler. Water quality is the key here, since any solid contaminants can cause a build-up of scale, which can act as unwanted insulation, impairing heat transfer efficiency and increasing the amount of fuel required to raise steam.
The two main sources of contamination are the feed make-up water and the returning condensate. Condensate returns to the boiler from the condenser, having been cooled using locally sourced, lower quality water. With condensers notoriously prone to leaks, cross-contamination is common.
Feed water on the other hand, is normally de-ionised, pre-heated, deaerated and chemically treated before it makes it to the boiler.
A failure in any one of these processes can lead to contamination problems. Regular boiler blowdown is the obvious way to control contamination, although dosing the feed with chemicals such as ammonia or hydrazine also stops some chemicals getting that far. Careful, continuous monitoring also plays a vital role in ensuring good long-term boiler chemistry.
So what should you look for? Typical parameters include: conductivity, pH, dissolved oxygen, sodium, silica, hydrazine, phosphate, ammonia and chloride.
6. Optimise the combustion process
Most waste heat is lost in the stack gases leaving the furnace. Creating conditions that generate the smallest quantity of flue gas at the lowest possible temperature will boost efficiency. This is because channelling extra air through the process simply carries more heat away in the flue gas. Obviously, hotter flue gas also ‘steals’ more energy than cooler gas, so that a 22°C drop in stack temperature can often boost boiler efficiency by one percent.
On the other hand, supplying insufficient air will result in incomplete combustion of the fuel. This leads to fouling of heat transfer surfaces and emissions of soot, smoke and carbon monoxide. So getting the air supply right is a fine balancing act. The optimum combustion process provides just enough excess air to completely burn the fuel. The right level of excess air depends on the fuel, but it ranges from between 5-10 percent for gas and 10-15 percent for fuel oil, all the way to 20-30 percent for stoked coal. Using instruments such as an ABB zirconia oxygen system and a temperature probe in the flue stack can ensure the plant is burning fuel optimally.
Furthermore, if the oxygen level rises in the stack-gas over time, it can also indicate the need for minor adjustments or repairs, while a rising stack-gas temperature can indicate the need for tube cleaning, since fouling may be hampering heat transfer.
7. Use measurement data to optimise your process
The ability to readily access energy consumption data for a given period or piece of equipment is a key first step in helping to create an effective energy management strategy.
Instrumentation by itself will not directly save you energy. What it will do, however, is help you to identify the areas where measures can be taken that will help you to optimise your energy consumption.
For example, data from a flow meter on a steam or process line can often be used as a preliminary measure when assessing whether to use a variable speed drive, which are proven to drastically reduce energy consumption. Similarly, data from other instruments, such as pressure or temperature devices, can often be used to measure the overall effectiveness of production equipment such as process vessels, with the data then used to help optimise the efficiency of that equipment.
8. Take good care of your instruments
Where instruments are already installed, it pays to make sure that they are kept at peak operating performance. To reduce the risk of failure or malfunction, it is advisable to ensure that maintenance, both in terms of frequency and procedures, is carried out in line with the device manufacturer’s recommendations.
Keeping instruments in good working order has been simplified by the latest generation of smart digital instruments, which offer an expanded range of possibilities for improved monitoring and control, by enabling operators and engineers to gain more useful information about the process and the device itself. With the arrival of wireless standards, such as WirelessHART, wireless adapters can now be fitted to existing HART instruments, providing a cost-effective and secure means of unlocking previously stranded data.
Modern instruments are typically more robust and more accurate. They are also easier to maintain, with features including on-board diagnostics enabling any problems to be quickly spotted and rectified, and are less prone to problems such as drift. It is important to remember though that nothing lasts forever. Even electrical components, can undergo a change in performance due to small chemical and / or physical changes with time. It is therefore advisable to have your instruments regularly checked and recalibrated if necessary to ensure they continue to deliver continued accuracy.
9. Site surveys
The Carbon Trust stresses that companies need to use a range of monitoring and targeting techniques to identify and implement energy saving measures. The Trust estimates that basic housekeeping enables many no- and low-cost savings, which can knock up to five percent or more off an industrial energy bill, while more formal energy management schemes can achieve savings of 20 to 30 percent or more, depending on which industrial sector a company operates in.
A site survey from a reputable manufacturer such as ABB is a recommended first step to manage energy use. It is a good way to identify wasteful processes that are easily rectified and offers advice and selection of products tailored for the particular application. Service and maintenance packages are also available to ensure the process is running at optimum efficiency.
10. Take the chance to spot other areas for energy saving
Many potential areas for energy savings can get overlooked. On older sites, for example, outdated or inefficient plant equipment could be consuming excessive quantities of steam or compressed air that could otherwise be reduced. By using instrumentation to monitor the performance of this equipment, informed decisions can be made on how to improve efficiency, either by refurbishing or upgrading it or investing in a replacement.
The same applies to the boiler itself. If the boiler is struggling or unable to the steam demanded by the process, or is consuming excessive fuel to generate steam, then this can be indicative of a need for servicing or replacement.
Summary
As a means of gathering constant performance data, instrumentation provides a vital first step in any energy saving regime. As a benchmark of current performance, instrumentation makes it possible to identify areas for improvement and to create the strategies needed to achieve it.
Source: http://www.zgsteamboiler.com/news/Ten-ways-to-better-steam-boiler-performance.html
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