Industrial Water Management
By Reducing Its Thirst for Water the Process Industry can Conserve Resources and Cut Cost
How well does industry manage water resources? The general tendency today is to take a holistic systems approach. More process water is being recirculated and industrial producers are recovering reusable substances and water treatment chemicals. Companies are also taking a new approach to effluent management. Partial flows are being diverted at an early stage, making treatment easier and less expensive. Technology is even available which can virtually eliminate effluent.
Plants, animals and humans depend on water for survival, but water is also an essential technical resource for industry - whether as cooling agent, transport medium, solvent or process water in a range of qualities from industrial water to softened or demineralized water to highly purified water for the pharmaceutical industry.
Industrial water consumption is not free. Inlet water normally needs to be conditioned, and treatment costs money. Circulation pumps consume energy. Post-treatment is also normally required so that the water can be re-circulated or discharged into receiving watercourses. For cost and environmental reasons, it is advantageous to reduce water movement, water heating and water contamination, and this is where industrial water management has a role to play.
Technological complexity is lower in regions where there is an abundance of water compared to parts of the world where water is scarce. The costs of closed-loop recirculation or even water-free production are more acceptable there than in countries like Germany. Whatever the water supply situation, production and water technology are always closely interrelated, creating the need for integrative technologies and water management systems.
Water Recycling and Elimination of Production Effluent
"Off-the-shelf" industrial water management does not exist. That is the conclusion reached in a ProcessNet position paper on the trends and outlook in industrial water technology, which was published in March 2014. Tailored strategies are needed for the specific industry, application and site. Water recycling based on recirculation of process water is normally only a viable option if contamination levels are low and water treatment is relatively inexpensive. Experts say that water recycling is less efficient for waste streams that are highly contaminated and/or contain substances that have a very diverse range of chemical and physical properties. The basic prerequisite for water recycling is the establishment of an efficient water management system to separate water that readily lends itself to recycling from water that is less suitable. Most of these internal recycling processes are located at or near the source where the complexity of the constituents is limited and additive techniques can be deployed with minimum effort and expense.
The integrated energy supplier Suncor Energy recycles more than 90% of the water contained in steam which the company uses to extract oil from oil sand. Instead of storing injection steam in underground disposal wells, recycled saline water is treated, the salts and solids are filtered out and the water is reused to produce steam again.
What Wabag is currently doing is another example. At the beginning of 2014, the company was awarded a contract to build a wastewater treatment plant at the new industrial park in the city of Al Kharj in Saudi Arabia. Effluent from various production facilities at the site will be treated to the maximum extent possible for re-use as process water. The plant will have a capacity of 10,000m3/d.
Zero Liquid Discharge - the Model for the Future?
Instead of purifying water to the extent possible prior to discharge, would it make more sense to eliminate water discharge altogether? Elimination of effluent from production (zero liquid discharge) is currently the subject of a highly controversial debate. 400 plants are already operating around the world. However treatment of the residual concentrates is problematic. Choosing a site with an abundant supply of water and implementation of an industrial water management program are generally preferable to the burdens associated with zero liquid discharge production which is very energy intensive. As a result, experts are pinning their hopes on tighter integration of water and energy management.
Bayer Technology Services has developed a process for handling effluent which contains organic matter as well as inorganic salts at an Indian pharmaceutical plant. The new stand-alone treatment process has three stages: the organic matter is removed by biological purification and the salt concentration is increased through reverse osmosis to minimize energy consumption in the subsequent evaporation stage.
Veolia Italy has developed a zero liquid discharge system for a global manufacturer of dispersions and adhesives that can treat 15 t/d of wastewater. In the first stage, a heat pump vacuum evaporator with forced circulation pre-concentrates the rinsing water. A vacuum evaporator with heat pump and scraper system in the boiling chamber then produces a final concentrate which is mixed with fresh dispersion to obtain a constant density. The distillate is treated for use in washing, reducing the wastewater volume to zero. What used to be a waste product that was sent for disposal is now re-used in the production process.
As part of the EU E4Water Project, currently the world's largest water management research project in the chemical industry, a number of plants in Belgium, France, Holland and Spain are working in unison to significantly reduce fresh water consumption. At Solvic and Dow Benelux, water flows from different plants are joined together. Treated effluent from one plant is used as feed water for another plant. The goal is to reduce fresh water consumption by up to 50%.
Membrane Process: Learning from Mother Nature
The use of membranes in water treatment technology has been on the increase for many years. There are good reasons why that is the case:
- Membranes run continuously and are fully automatic.
- Membrane materials are now cheaper and more effective.
- The membranes operate at lower pressure and that reduces energy consumption.
More than 2/3 of new desalination capacity being installed worldwide is now based on reverse osmosis. In contrast to traditional evaporation-based technologies, no heat energy is needed for this technology and thus the cost of desalinated water is reduced. Even in regions where energy costs are relatively low such as the Middle East, reverse osmosis is increasingly the solution of choice. Given the right plant design and the right equipment (60% of total energy consumption is used to power the pumps), nothing can match reverse osmosis technology, reports Sulzer.
Sea water is not the only option. Desalinated ground water is another potential source, for example in the dry American South, claims GTAI (Germany Trade & Invest). Texas, Florida and California are leading users of the technology. Seawater desalination is becoming an increasingly significant factor, particularly in California where megaprojects are in the planning pipeline. Demand for high-efficiency pumps and rugged membranes continues to increase. Financing for many projects is now provided by public-private partnerships.
Jim Taft, Executive Director of the Association of State Drinking Water Administrators (ASDWA), says that mobile desalination systems have very significant potential. Demand is likely to increase because these systems in the South could help the water industry to manage more frequent periods of drought or temporary supply shortages.
Some membrane system suppliers have now started to standardize their systems. Higher production volumes drive down the manufacturing costs for these plug-and-play solutions which are used to purify service water and drinking water and also for treatment of industrial wastewater. It takes minimal effort to connect the pre-assembled systems.
Recovery of Energy and Re-usable Materials
When there is direct contact, it is impossible to prevent production materials from contaminating the process water. As a result, the process water contains varying concentrations of contaminants (ranging from a few ppb to several %). If a substance can be re-used, recovery can make economic sense in addition to helping protect the environment.
The French startup Magpie Polymers has developed a highly efficient filtration method for capturing re-usable precious metals even if they are only present in minute amounts. Various filters made of polymer beads are installed, and the metals form selective bonds with the beads. The technique is already being deployed at several European companies.
The chemical group Lanxess also provides technology for recovering re-usable materials. Ion exchangers function as selective adsorbers for fine purification of wastewater flows and process electrolytes. Heavy metals and other substances such as boric acid, chromate, arsenate, fluoride and ammonia in salt solutions can be selectively captured.
Little use has been made so far of wastewater as a heat source. In the past, utilization of this energy was seldom possible, one of the constraining factors being the 65 °C flow temperature limit for heat pumps. Ochsner now markets high-temperature heat pumps with flow temperatures up to 100 °C, opening the door to totally new industrial and commercial heat pump applications.
Smart Use of Water
Resource conservation and economic considerations make it imperative to make intelligent use of industrial process water and to consume as little as possible. Water should not be transported, heated or contaminated more than is absolutely necessary to meet process needs. Water re-circulation and re-use are two crucial aspects of "smart water".
The article is based on a trend report commissioned by Dechema and written by international trade journalists. Industrial water management will be one of three focal topics at Achema 2015 on 15 - 19 June 2015 in Frankfurt, Germany. The world forum and leading trade show for the process industry brings together experts from a wide range of disciplines, institutions and generations to stimulate scientific exchange in chemical engineering, process engineering and biotechnology. Dechema is globally known as the organizer of Achema.