Industrial options assessed
NEL's Norman Glen on testing alternative water sources for industry
The price of water in the UK is continuing to rise, partly in response to UK and EU legislation which is enforcing higher water quality standards. While increased water quality for domestic consumption is highly desirable, for most industrial applications it is unnecessary and represents an additional cost. Although the use of appropriate quality water could minimise treatment costs and relieve demand on potable treatment plant, there are barriers to its wider application, such as user reluctance and supplier constraints.
In recognition of these issues NEL initiated the Sustainable Industrial Water Use project. With £900,000 of Department of Trade and Industry sponsorship and support from industrial partners at Grangemouth and Knowsley industrial complexes, the overall objective was to promote an integrated cross-sector approach to reducing the impact of industrial water use on water resources in the UK.
The project thus brought together major industrial water users, water suppliers, water treatment companies and environmental regulators. Two groupings were established: the Grangemouth Water Users Group (GWUG), comprising Avecia, BP, EniChem, Scottish Water, British Waterways, CalGavin, Ondeo Nalco and the Scottish Environment Protection Agency; and the Knowsley Water Users Group (KWUG) comprising Baker Petrolite, CP Kelco, Kodak, Sonea UK, United Utilities, British Waterways and the Environment Agency.
Grangemouth is one of the largest industrial complexes in the UK with major petrochemical industries concentrated in a small area. Water consumption is 71Ml/d, costing
business around £15M/pa at current charges. Most of the water is potable but used for a variety of purposes, including cooling, that do not require such a high water quality.
In view of the continuing increase in price for potable water several companies at Grangemouth were already actively looking at ways of reducing water consumption and the formation of GWUG was a logical step in addressing the overall aim of the project.
The Grangemouth area has many potential alternative water sources and one of GWUG’s first tasks was to review possibilities within reasonable proximity of the industrial complex.
One of the main uses of water at the Grangemouth complex is in heat-exchange systems. Fouling is the main cause of heat exchanger performance deterioration and over the past 20 years NEL has developed some specialised techniques for assessing the fouling potential of fluids, such as the Portable Fouling Assessment Unit (PFAU) and Process Fouling Monitor (PFM). A major part of the project was therefore concerned with developing and using this technology to assess the fouling potential of the most promising alternative supplies.
The PFAU and the PFM share the same principle of operation. A side stream of fluid is taken from a process stream and passed through a section of tubing representative of the material used in the process. The heat transfer rate of the section is then monitored under a range of flow and temperature conditions to simulate a range of conditions within the process plant ranging from typical to extreme. The PFM contains one or two test sections which can be run in series or parallel. The PFAU consists of nine test sections in three parallel flow lines and is ideally suited for undertaking parametric studies.
A significant number of the cooling systems at Grangemouth are closed-loop evaporative systems and a small evaporative cooling tower was therefore built and a complete closed-loop system constructed around the PFAU, as shown in Figure 1. The system was used to test sewage from Dalderse WwTW, water from the Forth and Clyde Canal and, for comparison, potable water. Each line in the PFAU was equipped with monitors constructed from 316 stainless steel, mild steel and Admiralty brass, thus simulating all the materials commonly used in the cooling circuits on the Grangemouth complex. Figure 2 shows typical data for three different waters at four cycles of concentration in stainless steel.
The experimental programme (using the PFAU and PFM units) along with other data, from water users and their water treatment specialists, suggests canal water will provide a suitable replacement supply equivalent to about 33% of current demand. Given the potential for reducing water demand at the Grangemouth companies – by leakage reduction, recycling and process changes – has already identified significant savings on water use, the new supply could represent the majority of future water requirements. This water would be well suited to cooling applications.
To meet demand over and above that which the canal could supply, two other routes may be available in the future – boreholes and WwTW outfalls. Based on the project data and additional information generated by the partners, it is likely that combining the three sources would provide sufficient water to meet process water needs at Grangemouth.
Following the successful start-up of GWUG the Knowsley group was established. The Knowsley Industrial Park near Liverpool is typical of many sites throughout the UK in terms of its mix of industrial tenants and their patterns of water use. Although the use of alternative supplies will play a role in moving towards sustainable industrial water use on such sites, it was also recognised general water reduction techniques would be important.
The work at Knowsley therefore focused on understanding the patterns of water use of the major water consumers, in terms of both volume and quality, to examine options for reducing total water use and minimising the amount of potable water used. This led to a series of recommendations for each of the companies and to the identification of a number of scenarios for the provision of a
site-wide non-potable supply. The approach used involves:
- understanding current plant operations,
- establishing which water sources may be available internally and externally,
- identifying critical items of plant and the effect of new sources on operability,
- establishing a hierarchy of water quality requirements,
- experimenting and modelling to predict operability effects,
- assessing costs of changes and payback periods,
- identifying barriers to change and planning to overcome them.
range of techniques including heat and mass balance modelling software and fouling monitors were used to carry out the work. For each of the industrial members of KWUG, a site survey covering the first four points previously listed was completed. The data was then used to construct heat and mass balance models of the sites. This provided information on minimising water use within individual sites and allowed an examination of the feasibility of providing an industrial quality water network to the park.
For the four sites studied the total water use is 785,000m3 per annum, made up of:
- 69% potable from mains supply,
- 29% from site boreholes, and
- 2% from rainwater.
Effluent disposal costs are significantly higher than the cost of water but the most significant utility cost is power. Although the supply of water is the lowest of the utility costs there is still scope to reduce water consumption and costs by using minimisation and reuse techniques and making further use of non-potable water. The estimated scope for the use of non-potable water is between 120,000 and 400,000m3 per annum.
For the three sites with significant effluent disposal costs there is scope for further reduction by cutting COD, since the Mogden formula takes strong account of the COD in determining the overall cost.
The data obtained from the initial visits clearly indicated there are opportunities for heat recovery within plants. In addition, combined heat and power (CHP) should be investigated. An integrated approach to utility provision and optimisation is more likely to yield cost-effective schemes but this would depend on the interpretation of the best practice guidelines for CHP plant.
From the outcomes of the work at Grangemouth and Knowsley, the project has achieved its key aim of demonstrating the benefits of an integrated cross-sector approach to industrial water use. Specific commercial opportunities have arisen from the project which have the potential to make a significant impact on industrial water use in the UK. However, although the Grangemouth complex is a very significant water user, general industrial water use throughout the UK is more typified by the Knowsley situation and further work, based on an integrated approach to utility use and optimisation, will be required to maximise the potential