The boiler house is the beating heart that circulates heat around most industrial processes.
With such a large installed base, many systems present scope to boost performance and reduce running costs, with great potential to save water and chemicals, minimise maintenance and reduce energy consumption and carbon emissions.
A lot of boiler and steam distribution system issues result from impurities in the feed water, so improving water quality is a great place to start, according to Chris Coleman, marketing product manager for condensate handling at Spirax Sarco.
On the waterfront
For example, he recommends considering reverse osmosis (RO) to remove minerals from the feed and eliminate boiler scale.
“It works by using semi-permeable membranes with pores so fine that 98% of all salts are removed from the incoming supply… this diminishes the need for boiler treatment chemicals, reduces ongoing maintenance costs, fuel consumption and water and energy losses, and makes RO a cost-effective way to maximise savings,” Coleman explains.
Whatever the feed water quality, boilers inevitably experience a build-up of dissolved solids over time and these must be purged periodically using a process called blowdown.
Blowdown expels hot, treated water alongside the impurities, so optimising blowdown is another way to save on energy, water and treatment chemicals. The best option is to automate the cycle by monitoring build-up of total dissolved solids (TDS).
“Automatic control systems measure the conductivity of the boiler water, compare it with a set point and automatically open a blowdown control valve if the TDS level is too high. This maintains a constant TDS level and minimises the loss of water from the boiler, as well as associated energy losses,” says Coleman.
He adds that it’s also important to get the overall water and condensate treatment regime right throughout the steam distribution cycle, not just in the boiler.
“Steam system conditioning can reduce chemical use, the risk of corrosion and maintenance costs, while increasing the reliability of the steam system. This results in greater productivity.”
Automatic control systems measure the conductivity of the boiler water, compare it with a set point and automatically open a blowdown control valve if the total dissolved solids level is too high
Chris Coleman, marketing product manager at Spirax Sarco
Other strategies for optimising the boiler house include recovering flash steam, which is generated when high-pressure condensate is returned to a lower-pressure boiler feed tank, for instance, or as the pressure in the boiler drops during blowdown.
A flash vessel is one method that can be used to separate flash steam from condensate, making it easier to recover the energy from both.
“Venting flash steam with no form of heat recovery wastes energy,” explains Coleman.
“By recovering flash steam and feeding it back into the feed tank via a deaerator head, companies can make economic and environmental savings,” he adds.
Heat can also be recovered from the boiler’s exhaust gases, although this can be difficult in systems burning heavy oil or biomass because the exhaust will be dirty and can damage conventional heat exchangers.
By recovering flash steam and feeding it back into the feed tank via a deaerator head, companies can make economic and environmental savings
Coleman recommends considering heat pipe technology if this is the case. Heat pipes are sealed units that span the wall separating the ‘hot’ exhaust stream from a ‘cold’ stream of gas or liquid.
Each pipe contains a working fluid that evaporates at one end and condenses at the other. This cycle effectively shifts heat from one side of the wall to the other.
Heat pipes are extremely robust and easy to maintain compared to standard heat exchangers.
A dirty exhaust is not the only challenge associated with using heavy fuel oil. Like coal, this carbon-rich fuel will inevitably lead to more carbon dioxide emissions than a methane-based alternative such as natural gas. What’s more, the fluctuating cost of heavy oil has also been a factor in the decision by some users to switch from oil to gas.
For example, the Tomatin whisky distillery in the Scottish Highlands recently chose Flogas Britain to convert a boiler from oil and coal to liquefied petroleum gas (LPG), since the distillery could not access the gas grid.
Tomatin initially tried to reduce its carbon footprint and fuel bills by introducing a biomass boiler – a fuel option previously unused in the Scottish distilling industry. However, the biomass system alone was unable to supply enough energy for the energy-intensive distilling process, so Tomatin was still left with a 10MW oil-fired boiler to meet the shortfall.
Tomatin general manager Graham Eunson says: “We needed a replacement for our oil boiler that would be cheaper to run, reduce our carbon footprint and be easier to maintain. The whisky industry is not keen on change, and we like to reduce risk as much as we can, so we spoke to colleagues in the industry who had already switched from oil to LPG.”
Flogas managed the installation of 12 two-tonne LPG storage tanks, along with pipework and burner installations. The tanks were located out of sight behind the distillery and the whole LPG system was up and running within a week.
Since installing the LPG system, Tomatin has enjoyed savings of more than 15% on its fuel bills. Original estimates predicted a return on investment of between 12 months and two years, but the system is now expected to pay for itself in just one year. Tomatin is also on track to reduce its annual carbon emissions by almost 20%.
“In addition to the financial and carbon savings we’re making, maintenance has been substantially reduced. The oil boiler required daily attention, but beyond the statutory safety checks, the new LPG system has been maintenance-free,” Eunson says.
The choice between adopting steam or thermal systems is determined by the requirements of the process and its temperature range
Carl Knight, managing director at Fulton Boilers
While steam is by far the most common industrial heattransporting medium, boiler manufacturer Fulton says that some applications could benefit from ditching steam altogether in favour of a thermal fluid-based system.
Thermal fluid systems use specialist oils as heat carriers and can therefore operate at atmospheric pressures up to 300°C. To reach a similar temperature using water or steam would require a pressure of 85 bar and that brings with it a host of maintenance requirements, including regular insurance inspections.
“The choice between adopting steam or thermal systems is determined by the requirements of the process and its temperature range. In general, if the process requires a temperature below 180°C, steam is usually the first choice. However, if the required process temperature is above 180°C, thermal fluid is often the better solution,” says Fulton Boilers managing director Carl Knight.
Controllability is another key advantage. For example, Fulton recently installed a system at the Rebellion Beer Company in Marlow. Rebellion’s Mark Gloyens says that Fulton’s new FT-C 240 vertical coil thermal system should save money on the company’s energy bills since it is now easy to turn the heater on and off as required with minimal heat-up time.
In contrast, the brewery’s old steam-based system needed to be turned on at the beginning of the day and left running, regardless of the demand for steam.