As a result, Dow and its partners now are twice reusing the community's treated wastewater through an innovative wastewater recycling program, thereby using every liter of water three times instead of once.
Today, Evides purifies 10,000 m3/d of municipal household wastewater for Dow, which uses it to generate steam and feed its manufacturing plants. Steam condensate serves in cooling towers until the water finally evaporates into the atmosphere. Compared with conventional desalination of seawater for the same use, recycling Terneuzen's wastewater cuts energy use by 95% — the equivalent of reducing its carbon dioxide emissions by 60,000 tons each year, says the company.
Not only is membrane separation inherently more energy efficient than desalination but using municipal effluent instead of seawater as the raw water source requires less driving force (pump pressure) to remove salt from the water because it has a lower salt content. In addition, the lower-salt-content effluent pares use and cost of chemical treatment of the membrane systems in half.
FOCUS ON ASSESSMENTS
In January 2011, Air Products & Chemicals, Allentown, Pa., had its water team begin work on water assessments in conjuction with GE Water, Trevose, Pa., its long-time primary provider of water treatment chemicals and services.
"The assessments are very focused on looking at operating procedures and so far we have carried out 25 globally. They are also very much focused on larger water consumers such as air separation and hydrogen conversion production facilities. Opportunities are identified by our operating staff working closely with GE Water," explains Julie O'Brien, Air Products corporate sustainability manager.
Overall, this had led to changes in two main areas. The first is an up-to-four-fold increase in cooling tower cycles — saving between 2 and 10% of water consumption, depending upon the facility. The second is greater use of recycled water, particularly for cooling.
Using this approach at Air Product's Santa Clara, Calif., HyCo hydrogen production plant has helped save 62 million gal/yr of potable water.
"At Santa Clara, we're using water that previously has been used by others and pre-treating it prior to use on-site. The main lessons from this site are that there are increasing opportunities for grey and recycled water to be used for cooling, and opportunities for greater water reuse within the facility — for example, using process condensate in the cooling tower makeup water (Figure 2). There have been other opportunities at other plants, but they're very site specific. For example, at one we are upgrading our monitoring systems to better quantify our ongoing water usage," notes O'Brien.
Air Products is sharing the recycling and reuse lessons learned at Santa Clara among its sites. In addition, the company is going beyond individual assessments to look more systemically at other strategies to improve overall water consumption. For example, it's developing technologies to reduce consumption and reuse water in water-constrained geographies. Initiatives such as the use of waste heat for water purification may influence the way it plans, designs and builds plants.
Overall, greater use of recycled water, combined with process improvements, enabled Air Products to decrease water consumption by 1.2 billion gallons between 2011 and 2012. The company already has met its 2015 water reduction goal but continues to focus on eliminating waste, increasing recycle and reuse, and offsetting water withdrawals from primary sources with reclaimed supplies.
O'Brien offers a cautionary note about how water is treated as a business cost: "First there was a push on carbon emissions, which led to questions about energy consumption and this, in turn, has led to questions about water consumption. They are all linked; so over time, more and more companies will likely appreciate that water scarcity and quality are business risks. At the same time, it may be difficult to justify water system improvement projects, such as the installation of pretreatment systems for recycled water, because water is not fully costed in many places, so the project paybacks might not meet hurdle rates. This will change as water rates increase."
A WATER STEWARDSHIP FIRST
On May 3rd, BASF, Ludwigshafen, Germany, set an industry milestone when its production facility in Tarragona, Spain, (Figure 3) became the first chemical site ever to achieve gold-level certification to the European Water Stewardship (EWS) standard.