Efficient steam system offers more sustainable operation
Following a steam system audit, a complete re-design of a dated system has helped a metal refiner to improved production levels, operate in a more sustainable way, and reduce energy costs by up to 60%.
The precious metal refining industry consumes significant amounts of heat and chemicals to extract impurities from noble metals. As a large user of chemicals and energy, London-based Vale Acton is always looking for ways to reduce its carbon footprint and to speed up process efficiency while reducing energy consumption.
Over the years Vale Acton had gradually updated specific sections of its steam system in to suit the various changes in production requirements. However, the majority of its steam network was in the region of 45 years of age. This not only limited process efficiency but the ageing pipework was also compromising safety and costing the business a significant amount in maintenance.
Recognising that improvements were needed to uphold the company’s commitment to the environment, Darren Matthias, project manager at Vale Acton, engaged with Spirax Sarco to find a solution.
While the refinery primarily uses steam for process heating, but it is also critical for many production processes too, including reactor vessels – both coil and jacketed – which are used to control the temperature of reactants, heater battery and tank heating applications, unit heaters, direct injection systems and steam hose stations for cleaning tanks, vessels, and process equipment.
Unfortunately, processes were impacted by both an out-dated condensate return system and boiler house which, in turn, were causing knock-on effects to other plant equipment.
“The condensate return system was inefficient and costly to operate which was becoming a major issue, with corrosion to pipework, as well as inconsistent water and blowdown quality problems,” said Matthias. “Condensate was returned to a common tank located in a tank farm which is extensively cooled by a plate heat exchanger before finally being sent to the effluent plant.
“We were using two boilers – one oil and one gas – to generate steam for the entire plant. Steam was generated in the boiler house at 3.8 bar g and the two boilers in question were operating at half the efficiency they should have been. This, coupled with an unreliable condensate recovery system, spelled a toxic combination of unsustainable operation and high costs”.
A detailed steam system audit helped to identify the specific issues which needed addressing, with its ethos for protecting its environment and staff being a key driver for this change. “Admittedly steam isn’t our core area of expertise, so we enlisted the help of Spirax Sarco to conduct a steam system audit,” said Matthias. “After analysing the entire system and completing a Hazard and Operability Study (HAZOP), the decision was made to design and supply new process steam, condensate and cooling systems.”
“Working with Spirax Sarco, we identified the problems and created solutions that would support our safety and environmental policies,” continued Matthias. Spirax recommended a complete design and supply of new steam, condensate and cooling water systems which would help streamline the steam network and improve process and production cycles.
New control valves, steam traps and condensate return units were fitted, with the addition of contamination detection systems – to bring the facility up-to-speed with current technologies.
Modular boiler house
Following the success of the initial project, the company invited Spirax Sarco to carry out the design and supply of its boiler house, replacing the burners with two efficient gas boilers.
“We were given two options to consider. We could either hire two boilers for a period of time while the upgrade took place in the existing boiler house, or, Spirax could complete the full design of the boiler house off-site. This meant the new boiler house could be assembled in a separate location so there was no disruption on-site,” said Matthias.
Two boilers fired only by gas were installed, as a more energy efficient and maintenance-friendly alternative to oil. The new boiler house is designed to allow a third boiler to be installed when Vale Acton are ready to increase capacity. An added benefit was that one of the new burners also allows the use of heat from a Combined Heat & Power (CHP) system, for efficiency.
New controls have also enabled staff to take back control of energy consumption. Data is now easily accessible, while improved visibility of energy consumption has allowed the company to track their environmental impact more effectively.
“By replacing the oil and gas burners with two gas boilers we have saved a significant amount in energy. We are achieving 55% less nitrogen oxides (NOx) emissions than we were from our old oil boiler and we’re also proud to be emitting zero sulphur oxides (SOx),” said Matthias. “Since switching to gas have seen a 60% cost reduction and a considerable improvement in our operational efficiency. This has resulted in a faster process cycle and production levels.”
Safety is a key priority for the firm so the installation of double, block and bleed isolation valves has been an added benefit, allowing for safe maintenance to take place during production. In addition, employees were provided with an on-site Boiler Operation Accreditation Scheme (BOAS) course to ensure that safety and efficiency is always prioritised by staff. >
Source: Control Engineering Europe - All Articles