Full steam ahead for quality energy management
Published: 28 March, 2018
With the emphasis now very much on finding ways to manage energy more responsi-bly, both for economic and environmental reasons, using steam more efficiently is vital to reducing costs and boosting green credentials. David Bowers, product manager pressure and process flow for ABB Measurement and Analytics, explains why vortex and swirl flowmeters are ideal for steam measurement applications.
Rising fuel prices and increased pressure to minimise the use of fossil fuels are forc-ing industrial organisations to re-evaluate their steam distribution systems to find new ways to improve efficiency and reduce costs. To achieve this, steam use needs to be monitored accurately and continuously to ensure it is being used as productively as possible.
High energy prices continue to have a major impact on the UK’s industrial companies. Compared with other EU member states for example, the UK pays well above the aver-age, with only Denmark paying more for its energy.
With the price of energy predicted to continue rising, major energy users such as water companies, food and beverage factories and the data centres used by huge telecoms and technology businesses are in line for another massive price hike. Currently, any organisation that sits in the top 10 highest energy users pays roughly £120m per year for electricity, with some estimates pointing to a further 42% rise in future years at cur-rent consumption levels. (Source: Daily Telegraph, October 29th 2017 - British industry faces an energy cost crisis - and it is set to grow).
Large multinationals are looking to reduce their reliance on power from the National Grid by generating their own electricity using small-scale power generation projects. However, many businesses have neither the space nor the capital to embark on similar schemes.
Anticipated cost increases are now pushing companies to reassess existing industrial processes and explore other methods of saving money and improving efficiency. One key area in which savings can be achieved is in the generation, distribution and con-sumption of steam.
The UK Government has its part to play in this process. A government initiative: the Non-Domestic Renewable Heat Incentive (RHI), for example, applies to plants that use either liquid or steam as the main heat delivery method. Businesses are encouraged through financial incentives to improve process efficiency and invest in more sustain-able fuels to produce steam.
Being able to better understand how much steam is being distributed through a system and the amount that is being consumed allows operators to obtain a clearer picture of potential cost implications. By helping to identify potential areas for improvement, the burning of fossil fuels can also be efficiently controlled, helping to reduce harmful emissions and the overall carbon footprint of the site. In addition, accurate monitoring can spot any existing issues, such as leaks, which can contribute to huge revenue loss if not promptly identified and fixed.
To monitor steam or gas applications accurately, it is not sufficient to determine the ac-tual volume flow of the steam to ascertain the amount of energy that is travelling through the distribution system. In the majority of cases, establishing the mass flow of the steam is needed.
In order to measure mass flow it is critical to use the appropriate meter. Although differ-ential pressure meters can do the job, they require additional equipment such as flow computers, differential pressure and temperature transmitters mounted on orifice plates, pushing up the cost and time of installation and increasing the chance of un-planned maintenance.
A better way of measuring steam flow
To reduce cost and maintenance concerns, a better option is to use Vortex or Swirl me-ters as both offer superior accuracy compared to alternative methods, particularly in applications where the flow range fluctuates. Flow measurements are as accurate as +/- 0.5 percent, with turndown – the range over which the flowmeter can accurately measure - being 10 times greater compared to using more traditional orifice plates.
Achieving accurate monitoring of steam distribution systems is achieved by both me-ters forcing steam to rotate or form eddies. Swirl meters have static veins installed which aid the creation of steam rotations. The frequency of the spiralling rotations that are created are then measured. In comparison, vortex meters are slightly different as it is the frequency of eddies that is measured. These eddies or vortices are created due to an intentional obstruction that is installed within the meter called a shedder.
Furthermore, both meters contain two piezo elements to cancel vibrations as well as a special algorithm that guarantees consistent handling and accurate monitoring even in harsh applications.
As the frequency of the vortex street in a vortex meter and of the secondary rotation in a swirl meter are each directly proportional to the volumetric flowrate of the fluid, there is no need to compensate for changes in pressure, temperature or density. The meters only need to know the temperature of the steam to calculate the mass flow.
When measuring direct mass and energy, ease of installation is key. Swirl meters are especially simple to install, particularly when companies are looking to retrofit a meter to an existing system. The swirl meter is perfect for this as it can be installed virtually anywhere. In most applications, flowmeters need an uninterrupted flow either side of an obstruction such as a valve or bend to effectively monitor the process and record precise readings. With swirl flowmeters, just three and two pipe diameters upstream and downstream of an obstruction are needed, with no need for additional flow straighteners, making it ideal for installation in those locations in which space is at a premium.
The best models have their own built-in computers. For example, both ABB’s Vor-texMaster and SwirlMaster flowmeters feature flow computers that can be used to pro-vide extremely accurate energy measurements. Steam pressure, temperature and vol-ume are used to calculate a mass flow reading, from which an energy measurement can then be derived.
The benefits of being able to measure temperature, pressure and volume using a sin-gle device in energy management applications are demonstrated by the following ex-ample. With saturated steam of 6 bar absolute at a temperature of 159°C, the correct density should be 3.1817 kg/m3. With slight overheating of the steam to avoid con-densation forming, for example by 2°C at a constant pressure, a density of 3.3383 kg/m3 would be used for the mass calculation without taking the pressure into account.
This would lead to a density and mass error of around 5%. Assuming a cost of £50 / MWh and an energy flow of approximately 3 tonnes per hour (for DN100 piping and 50% load), this five percent error could incur additional costs of around £4500 per month.
This error can be virtually eliminated by factoring in pressure and compensation to en-sure that the steam state is measured accurately and reliably.
Measure, optimise, save
Having access to accurate information about the steam and hot water flows around a site is a tremendously powerful tool for monitoring and controlling energy use, making strategically positioned meters the front line in high quality energy management sys-tems. The inherent benefits of vortex and swirl flowmeters make them an ideal way for companies to spot potential areas for improved energy efficiency and environmental performance and significant improvements in their bottom line.
