Many chemical makers now are focusing intently on water issues, prompted by concerns over water supply, quality and cost as well as by the quest for improved sustainability. As the experiences of Dow, Huntsman, Bayer and AkzoNobel show, optimizing water use requires careful analysis of all production processes involved.
“Changing water source is effectively a change in raw material and, therefore, numerous checks have to be carried out before it can happen,” cautions Verónica García Molina, EMEA technical service and development manager, and global water technology center R&D manager, Dow Water and Process Solutions (DW&PS), Tarragona, Spain.
Huntsman Corp., The Woodlands, Texas, notes that an accurate and comprehensive view of plant water use must underpin efforts. At its facilities in drought-stricken Texas, nothing has escaped attention: “To meet the water authority’s call for conservation, operating personnel at the Port Neches plant, located 100 miles east of Houston, went through every unit to identify areas for reducing or eliminating water use, including replacing leaking valves,” notes Mike Miller, senior manager, environmental, Huntsman Port Neches operations.
Dow’s technology center in Tarragona (Figure 1) focuses both on development of technologies to improve water treatment and on process optimization and integration needed to implement them to the best effect. An ongoing water optimization project at the Camp de Tarragona chemical complex exemplifies a successful combination of the two.
The Tarragona region of Spain traditionally suffers rainfall shortages. The chemical complex takes water from the River Ebro, one of the most important rivers in Spain. The river also supplies the Camp de Tarragona municipality, which is popular with tourists; the local population of 200,000 can triple to 600,000 in a busy season. Unfortunately, drought and demand have caused a 25% fall in river volume over the last 60 years.
For its part, the chemical complex draws 19,000m3/h of water from the Ebro. Home to almost 30 chemical companies — including a Dow facility that manufactures olefins, polyolefins, polyglycols, surfactants and performance fluids — and employing over 33,000 people, the site produces more than 21 million mt/y of products; it is the most important chemical complex in the Mediterranean region.
Backed by almost €6 million ($6.7 million) in funding from the DEMOWARE water reuse initiative of the European Union (EU), the complex in 2014 started a project aimed at replacing river water with treated wastewater from the municipality.
For Dow, this meant cutting back on the 6 million m3/y of river water it alone used.
Today, Dow relies on a blend of 40% reclaimed water and 60% Ebro water. The plan eventually is to raise the level of reclaimed water in the blend to 90%.
“There were questions and concerns about the impact of the change in areas like corrosion, scaling and biofouling or bacteria growth phenomena. We reached a common agreement with the plant after about six months of a deep review process which included failure modes and effects analysis,” says Molina.
Some surprises have occurred. For example, with the current 40% reclaimed water blending, DW&PS projected a 20–30% reduction in blowdown water production by the plant processes because of the better quality. In fact, the drop is nearly 50% now, which has cut the cost of treating the resulting wastewater, too.
The current 40% blending also has pared the volume of chemicals needed in cooling towers by about 23%, again because of the higher quality water. Dow expects to increase the amount of reclaimed water used in its ethylene-cracker cooling tower to 90% over the next 2–3 months.
“The expectation is that with better water quality we will also see additional benefits and savings due to less fouling buildup that, in turn, will lead to a decrease of cleaning operations in heat exchangers and other plant equipment,” adds Molina.
One innovation stemming from this project is the idea of using DW&PS’ minimal liquid discharge approach as part of the cost/benefit analysis. This enables an increase in the recovery of a system from 70% (achievable using a standard reverse-osmosis configuration) to as much as 95% at a 60% lower cost compared to alternative technologies such as zero liquid discharge, says Dow.