David Hayes describes why health estate managers recognise their responsibility to reduce carbon dioxide emissions and meet ever more stringent statutory environmental requirements. To help reach these goals, a range of advanced environmental technologies are available to reduce pollution and energy consumption. One such technology is the HVD process from Environmental Water Systems (UK) Limited (EWS). This article looks at the softening process and its use within the healthcare sector and the benefits of using HVD technology.
Proven throughout Europe, HVD technology efficiently softens water to remove dissolved calcium and magnesium ‘hardness cations’ that cause scum and lime scale within process and drinking water systems. Manganese and ferrous iron ion concentrations, present in certain water supplies, are also reduced by the HVD process depending on levels present in the feed water.
Hardness causes two main undesirable effects. Most visibly, the dissolved positively charged hardness cations react with soaps and calcium-sensitive detergents, hindering their ability to lather and reducing the effectiveness of detergent formulations. A precipitate is formed - the familiar ‘bathtub ring.’
In the healthcare industry, softened water is typically required in the feed to low pressure boiler systems. Without water softening, calcium and magnesium carbonates will precipitate as hard deposits on the surfaces of pipes and heat exchanger surfaces. This results primarily from the thermal decomposition of calcium bicarbonate and magnesium bicarbonate. The resulting build-up of scale can restrict water flow in pipes. In low pressure boilers, the deposits act as an insulation that impairs the flow of heat into the water, reducing heating efficiency and allowing the metal components in the boiler to overheat, leading to failure of boiler components.
Various crystalline forms of calcium carbonate can be deposited (such as calcite or aragonite) and the extent of damage can be variable. The nature and variability of the feedwater and relative concentrations of the different positive hardness cations (calcium, magnesium, manganese and iron) and negative anions (such as bicarbonate, sulphate and phosphate), along with the boiler pressure and temperature, allows us to predict the extent of damage that will result to metal components. EWS have a detailed understanding of these chemical considerations. Their process engineers can effectively design HVD softening systems to meet these site specific considerations. Clearly, effective water softening is required to avoid any damage to water heating systems.
The water to be treated passes through a bed of ion exchange resin in a batch process known as Base Exchange softening. This has two modes of operation. In Service mode the feed water passes through the resin and the hardness cations are removed. In Regeneration mode, a brine solution is pumped through the resin, transferring the hardness cations to the waste stream thereby removing them from the process.
In Service operation, negatively-charged ion exchange resins absorb and bind the hardness cations, which are positively charged. The resins initially contain monovalent (containing a single charge) sodium or potassium cations, which exchange with the divalent (containing two charges) calcium and magnesium hardness cations in the water. As the water passes through the resin column, the hardness ions replace the sodium or potassium ions which are released into the water in exchange. The harder the water, the more sodium or potassium ions are released from the resin and into the water.
As the ion exchange resins become loaded with the undesirable hardness cations they gradually lose their effectiveness and must be regenerated. In Base Exchange Softening, Regeneration Mode is undertaken by passing a concentrated brine solution through the ion exchange resin. Usually sodium chloride solution is used as the brine but potassium chloride can also be utilised. Most of the salts used for regeneration get flushed out of the system and may be released into the sewer or local environment. These processes can be damaging to the environment, and consequently waste volumes and concentrations need to be minimised.
Traditional approaches to boiler feed treatment and other healthcare uses for softened water have been dominated by outdated Co-Current softeners, where both Service and Regeneration flows run in the same direction, from the top of the softener to the bottom.
The HVD system is a superior replacement to these outdated Co-Current systems. The advanced technology is based on Counter-Current operation which utilises specialised ion exchange resins to achieve a regeneration flow in the opposite direction to the Service flow, i.e. from the bottom of the softener to the top.
Figure 1 - HVD water softening installation
HVD Technology
The fully automated HVD system can typically pay back capital cost in less than eighteen months from savings in operational cost, when replacing Co-Current systems. This self-funded green technology enables plant managers to quickly realise many environmental benefits and save time and money.
With an HVD system, salt usage is reduced along with rinse water consumption and the consequent wastewater volumes. The more efficient Regeneration mode reduces energy consumption and environmental impact is minimised because less waste is produced, less salt is used and less energy is required. The overall carbon footprint of the softening process is therefore reduced.
The HVD process has been developed to meet the increasing global demand from a range of industries for an enhanced and cost-effective Base Exchange softening process through the use of Counter-Current technology. Until recently, traditional Co-Current systems had typically been used in the majority of water softening projects. Their performance, in terms of treated water quality and cost-effectiveness, is significantly inferior: environmental impact is higher because the Regeneration Mode is typically much less efficient.
HVD Technology has the following benefits when compared to these outdated and inefficient Co-Current softening systems:
Reduced salt requirement
Use of advanced ion exchange resins and the special design of internal water/brine distribution systems coupled with the precise measurement of salt usage, reduces the quantity of salt required per unit water treated.
Reduced rinse water consumption
Precise measurement of rinse water conductivity minimises the quantity of rinse water required by stopping the rinse cycle as soon as the desired quality is met. This is in contrast to outdated system designs where rinsing is left to run on a fixed timer regardless of rinse water quality.
Reduced wastewater production
Because there is less rinse water, the volume of wastewater produced by the HVD process reduces accordingly.
Reduced energy consumption
As the regeneration process is more efficient and less pumping power is required to transfer brine and move the wastewater, overall energy consumption is reduced.
Reduced environmental impact
Because there is less waste, less salt used and less energy required, the overall environmental impact is substantially reduced. This reduces the carbon footprint of this green technology.
Reduced operator time
The use of an integrated and automatic control/monitoring system within the HVD system eliminates constant operator attendance and significantly reduces the time required to monitor the operation of the process.
Reduced maintenance requirements
The HVD design, containing fewer components, reduces ongoing maintenance requirements.
EWS Expertise
HVD softening equipment can be included in a range of additional applications, such as in laundries or as a pre-treatment to other technologies that produce high purity water, such as reverse osmosis membrane systems. All these complimentary technologies are designed into process systems, installed and maintained by Environmental Water Systems (UK) Limited, taking into account specific site conditions.
EWS is well respected as a leading provider of water treatment technology solutions, including the HVD process. Services include development of design concepts, laboratory trials, pilot trials, process engineering design, production control, commissioning, maintenance, optimisation, servicing, provision of spare parts and consumables, and plant operation.
In addition to the provision of packaged HVD plant for softening applications, the expanding team of process engineering professionals at EWS will evaluate individual projects on other applications based on specific site conditions and project requirements. Their detailed investigations are then used to produce preliminary design concepts for further discussion with clients at the feasibility stage.
To assist with these feasibility studies, EWS is able to arrange a variety of tests to characterise water and waste streams using various specialist laboratories. Pilot systems and associated pre- and post-treatment technologies, can be used on a variety of problem water and waste sources. Experienced process engineers operate and optimise the pilot trials and use the results obtained to develop detailed engineering designs.
Pilot tests are excellent diagnostic and optimisation tools. When customers are experiencing problems in the field, or want to further optimise their process, pilot plants can be set up to run in parallel with the main system. They can be used to help determine the cause of the failure and conduct onsite in-stream performance testing analysis. Rental of pilot systems helps identify solutions, improvements or optimisations that can be applied later to the entire plant, and all this can be done without affecting the main process.
The information gathered through design concept development, laboratory and pilot scale tests is used to develop detailed process engineering designs. Advanced computer software packages are used to model process systems and develop computer aided designs. EWS are able to manufacture and assemble containerised and skid-mounted components in their fabrication facilities, and they also undertake pre-delivery testing of process and control systems as standard prior to despatch. Tests can be witnessed by clients as necessary. This results in less time required on site for installation and commissioning activities.
Dedicated process engineers provide a friendly and professional on-site service which involves full process commissioning and optimisation of systems. Proving tests and ongoing performance trials are supervised as required. Comprehensive maintenance schedules and servicing packages tailored to specific project requirements can be provided, along with detailed project-specific price lists of spare parts and consumables specifically required for individual projects.
Conclusions
By switching to advanced modern environmental technologies such as the HVD Counter-Current base exchange water softening process, health estate managers will be able to address their responsibility to reduce CO2 emissions and meet ever more stringent statutory environmental requirements. Compared to outdated Co-Current softening systems, the HVD process from Environmental Water Systems Limited (EWS) provides a self-funded green solution that enables plant managers to quickly realise many environmental benefits, reducing overall carbon footprint whilst saving time and money. Salt usage is reduced along with rinse water consumption. More efficient regeneration reduces energy consumption and environmental impact is minimized because less waste is produced, less salt is used and less energy is required.
Author Details
David Hayes is Sales Director at Environmental Water Systems (UK) Limited. For further details on HVD technology and EWS call + 44 (0)1934 741782 or visit www.reverseosmosis.co.uk.