|Water being dispersed across the tube bundle of an |
The industrial sector is diverse and uses water in a variety of ways. Some water uses are common to many industries, for example the use of water as a cooling medium and for the production of steam. Other water uses are very specific to individual industries, for example the use of water as a chemical carrier and rinsing medium in electroplating. The industrial sector has the potential to consume large volumes of water, as well as the potential to contaminate large volumes of water, with both of these impacts reducing the amount of water available to downstream users. The links between industry and the preservation of water resources are therefore indisputable, even for industries which on the face of things are not considered to be water-intensive.
In the industrial sector, water is not only linked to energy, but also to material usage, air quality, health and safety, product quality and other performance dimensions. The relationships may be virtuous or conflicting. Some examples from various industries are outlined in the table below.
Table 1: Links between Water Use Efficiency and other Operational Goals
Heat recovery through process integration reduces waste heat and hence cooling tower evaporation. Energy efficiency and water use efficiency work in concert.
Material usage and energy efficiency
Increased water usage at lautering increases extract recovery. Increased evaporation rates at boiling could be required to achieve desired sugar concentrations, increasing water and energy use in order to achieve the material usage benefit.
Coal-fired Power generation
Wet flue gas desulphurisation (FGD) technologies consume a significant amount of water, but reduce sulphur dioxide and mercury levels in flue gases. The effluents produced must be safely handled to reduce groundwater contamination risks to avoid transference of the risks from air to water resources.
Pulp and paper
The quality of bleached pulp is partly dependent on the amount of water used for pulp washing. In the absence of recycling, water use and product quality oppose each other.
Water is used for cleaning-in-place (CIP), where processing equipment is cleaned and sterilised to prevent microbial contamination of food products. Increased cleaning generally requires more water.
Product quality and effluent volume
Rinses downstream of process baths reduce the carryover of chemicals into successive baths, reducing impurities and improving product quality. Improved quality is a function of water usage, but increased rinsing will increase the volume of effluent produced.
These are just a few examples, and one could get into a lot more detail when examining issues at the industry level. The point here is that in many industries, water usage has to be managed against the backdrop of a large portfolio of constraints of which energy is just one.
Within individual industries, the amount of water used is also heavily dependent on technology choices. These come with trade-offs. For example, a site that employs dry cooling devices will enjoy a reduced consumptive water use over comparable sites that employ wet cooling systems. However, in warm weather dry cooling devices may lack sufficient cooling capacity. In the case of power generation, this translates into reduced turbine efficiency and ultimately, increased emissions.
Quantitative benchmarking of water usage in the industrial sector, if injudiciously carried out, can lead to wildly incorrect conclusions. Consider that product mix typically has an enormous impact on water consumption, and hence that within individual industries, sites producing different products cannot be compared fairly without product-specific benchmarks. A paper mill producing fully bleached Kraft pulp could easily use twice as much water per ton of production than a mill producing newsprint for example. And of course the issue of technology is important given, as mentioned above, that different technologies imply different water use characteristics. This is not to say that benchmarking is not useful, since every site does need to understand the envelope of what’s possible, both within the constraints of their own technological footprint and product mix and in terms of what could be delivered by alternative technologies. Consider however that not all technologies are equal in terms of the other water-related outcomes of interest mentioned above. Given that water is generally a cheap commodity relative to raw materials, and that product quality problems can be very costly, industrial players will tend to favour performance on these issues, as well as non-negotiables such as safety, over water use efficiency.
To complete the picture of what the challenges of efficient industrial water management entail, consider that the industrial environment is never static. Raw material quality changes continuously, particularly where industries use natural resources, such as in mineral processing and agro-industries. Components fail, even where good preventive maintenance practices are in place. Employees make mistakes, even where automation and mistake-proofing techniques have been applied. Atmospheric conditions vary. All of these variations have a material effect on water consumption, and the most efficient operators are those who design out variation as far as possible and have robust systems in place for identifying risks and responding to non-conformance.
Given all of these complexities, how does the operator of an industrial concern set about minimising water consumption? Minimising water usage in this context requires deep industry-specific knowledge, without which there is a tremendous risk of incurring unintended consequences. And this is precisely why the regulation of industry from a water use perspective is such a daunting task for policymakers. What should be clear is that industrial water conservation is not simply a case of “closing the tap”. Since water use impinges on so many other critical operational objectives, industrial water conservation has to be tackled in an integrated fashion that balances material usage, safety (for employees, local communities and consumers), hygiene, product quality and environmental considerations. And this is true for every individual aspect of industrial sustainability and sustainability in general. I will get into more details regarding specific aspects of industrial water conservation in future posts, so stay tuned.