WATER SYSTEM MANAGEMENT
How RO feedwater can boost boiler performance
Paul Godfrey, managing director at Puretech Water Systems (UK) – a designer, manufacturer, and installation/maintenance specialist in water treatment systems – considers the key benefits of reverse osmosis (RO) water as feedwater for boilers, and how its use in this context facilitates reducing boiler blowdown periods.
The drastic rise in energy costs has left many Estates managers looking for avenues that lead to cost savings across their department. Sustainable water management has also become a priority issue. The Department of Health published Health Technical Memorandum 07-04 (HTM07-04) in 20131
to serve as
guidance to Estates teams for best practice measures and provide advice on sustainable water management. Reducing wastewater and investigating technologies that positively impact a change are actively encouraged. NHS Property Services echoes this sentiment with a directorate and pledge to becoming more water-efficient and reducing wastewater.2
Steam boiler plants
Boilers are important components for heating applications, and water is the most used fluid in these heating processes, primarily due to its relative abundance and high heat capacity. Large amounts of water are required, and often there is potential for water saving. This saving results in lower water and sewer bills and decreased treatment costs. Boiler feedwater quality control is a pragmatic approach being taken by many to reduce costs while simultaneously improving the energy efficiency of the steam boiler system.
The feedwater received by the boiler consists of a varying proportion of recovered condensed water (return water) and fresh water, which has been purified in varying degrees (‘make-up water’). The make-up water is usually natural water either in its raw state or treated prior to use.3
Feedwater composition therefore depends on the quality of the make-up water and the amount of condensate that is returned to the boiler. The steam, which escapes from the boiler, frequently contains liquid droplets and gases. The water remaining in liquid form at the bottom of the boiler picks up all the foreign matter from the water that was converted to steam.
72 Health Estate Journal November 2021
Steam boiler systems are an area where Estates managers in hospitals and other healthcare facilities can assess and improve efficiencies.
Blowdown
These impurities must be blown down by the discharge of some of the water from the boiler to the drains. The permissible percentage of blowdown at a plant is strictly limited by running costs and any initial outlay. In order to mitigate maintenance costs, it is considered best practice to reduce this percentage to the smallest figure possible to improve a site’s environmental impact by reducing wastewater with less frequently occurring blowdowns.
Feedwater – sources and variations Boiler feedwater treatment is an integrally important part of operating and maintaining a boiler system. As steam is produced, dissolved solids become concentrated and form deposits inside the boiler. Over time, this invariably leads to poor heat transfer and reduces the efficiency of the boiler. Dissolved gasses
such as oxygen and carbon dioxide will react with the metals in the boiler system, and will ultimately lead to boiler corrosion. Excessive levels of impurities cause this corrosion, inhibiting the boiler’s efficiency in heat transfer. It also affects the overall distribution of the steam around the system. Impurities that are often present within the system include, but are not limited to: n Alkalinity (CaCO3
). n Carbon Dioxide (CO2 ).
n Calcium (Ca). n Calcium Phosphate (Ca3
n Chlorides (Cl). n Hydrogen Sulphide (H2
n Manganese (Mn). n Magnesium (Mg). n Iron (Fe). n Oxygen (O2
).
n Silica (Si). n Sodium (NaOH, NaHCO3 n Sulphates (SO4
). , Na2 CO3 ). (PO4 S). )2 .
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