Higher energy efficiency ranks as a top priority in many chemical makers’ efforts to enhance sustainability and competitiveness. As the ongoing experiences of companies such as DuPont, AkzoNobel and Eastman show, improvements can come in a hugely diverse number of ways, from process redesign to better lighting.
For example, DuPont, Wilmington, Del., made a significant process change in the Delrin Chemical Area (DCA) at its site in Dordrecht, the Netherlands (Figure 1), which is home to nine manufacturing plants where refrigerants, synthetic resins and powder coatings are produced. The DCA is the largest consumer of steam at the site. One of the main steam consumers in the DCA is a concentrator column that reworks a number of recycle formaldehyde/water steams to give a formalin solution for re-use in the Delrin (an acetal resin) process. The excess water goes to a waste treatment facility.
“To reduce the energy consumption of the concentrator column, a project was started to operate the concentrator column in a more-energy-efficient mode,” explains Eelco de Visser, operations supervisor, Delrin compounding.
A simulation prompted a proposal for a process change — to split the recycle streams of aqueous formaldehyde that were collected in a feed tank and then fed to the column. These recycle streams come from various sources and vary in formaldehyde concentration. The largest volume stream, the “extraction tails flow,” has the lowest formaldehyde concentration (1.5–2%). The remaining recycle streams have much higher formaldehyde concentrations, ranging from 10 to 20%. The revision involved feeding the low-formaldehyde-content stream separately at a new, lower feed point in the concentrator column.
The modified process has been in continuous operation for over a year now with optimization still ongoing.
The upgrade has reduced steam consumption in the concentrator column by 16,7000 tons/yr with a saving of €418,000/yr ($466,000/yr). Substantial savings also have come from the associated decrease in CO2 emissions. “The total savings overall add up to €466,000/yr [$520,000], all for an invested capital of €436,000 [$487,000],” adds de Visser.
DuPont’s Spruance plant in Richmond, Va., which has been in operation since the 1920s and today manufactures textile fibers, also has achieved substantial energy savings as part of its efforts to cut emissions. The site revitalized its energy conservation/efficiency program through participation in the certified energy auditor training program,” notes John Kane Jr., principal consultant for DuPont Engineering Technology/Energy Engineering. Energy savings are estimated to have exceeded $4 million over the last five years.
Going Beyond The Fenceline
In Grindsted, Denmark, DuPont Nutrition & Health was screening possible energy saving projects for its site when it discovered a major potential win-win situation.
Surplus heat from production was being sent to cooling towers (Figure 2). The energy team decided to make better use of this surplus heat by selling it to the Grindsted electricity and heating plant (GEV), which delivers heat and electricity to private households and other buildings for water and space heating during winter.
“District heating is common in most cities in Denmark as they are densely populated, with little sprawl. This makes it possible to produce heat efficiently at combined heat and power plants and subsequently supply this to customers through a network of insulated pipes,” explains Martin Kirstein Madsen, Grindsted site manager.
The DuPont plant now supplies an estimated 12,627 MWh to GEV, enough to power 900 homes. It also saves GEV 1.2 million Nm3/yr in natural gas use. This translates to an annual reduction of 2,700 tons in CO2 emissions at GEV and a decrease of 70 tons at the Grindsted site.
“This project shows that it is possible to find win-wins for both the economy and ecology. Furthermore, it is an example of industrial symbiosis where a byproduct initially perceived as waste in one company can be turned into a valuable resource input for another company,” adds Madsen.
AkzoNobel, Amsterdam, the Netherlands, does not have a specific energy target but tracks energy use with a metric called the Eco Efficiency Footprint, which incorporates nine parameters, one of which is energy used per ton of product.
Peter Nieuwenhuizen, AkzoNobel’s RD&I director specialty chemicals, Utrecht, the Netherlands, cites an operational eco-efficiency program carried out at the company’s surface chemistry plant in Stenungsund, Sweden. The ethylene oxide manufactured there goes into a variety of products including detergents, asphalts and mining chemicals.