The team also identified a number of other projects that offered somewhat longer payback but were definitely worth considering:
- Adding a blowdown heat-recovery exchanger. Blowdown was going to a flash tank to recover low pressure steam but lack of heat exchangers in the system meant that lots of thermal energy was still being lost. Putting in an exchanger upstream of the tank would enable capture of significant heat that could be used to preheat boiler makeup water. This would save about 31,000 million Btu of gas and $200,000.
- Preheating reactor feed with 75-psig steam. Replacing some of the 600-psig steam being used wouldn’t save natural gas but would allow more on-site electricity generation from the higher-pressure steam. This would reduce electricity purchases by almost 1,280 M Wh and nearly $80,000.
- Installing a back-pressure turbine drive. The site generates 600-psig steam but most applications only require 200-psig steam. Putting in a back-pressure turbine drive could generate electricity to power some critical equipment and save around 1,950 M Wh and more than $120,000.
The estimates the team developed using SSAT came very close to the benefits Dow actually achieved for the near-term projects. The steam-trap repair project provided annual energy savings of 109,000 million Btu and about $800,000 in costs. Efforts to combat leaks led to annual savings of 163,000 million Btu and more than $1.1 million. Implementation costs for both programs totaled about $225,000, so payback was achieved in little more than six weeks! Steam trap maintenance and leak management are now ongoing programs.
In the short-term, insulation inspection and repair is still being conducted with a minimum mandatory visual inspection of all plant distribution lines every three years. In addition, a condensate project has been planned and is part of the new capital spending plan for implementation in 2009.
Medium-term and additional long-term Dow driven energy efficiency and conservation projects have been captured in an opportunity tracking system and will be made part of the plant specific technology plan. These opportunities will be further developed and could be part of future capital spending plans.
Jason W. Gathright is senior improvement specialist, energy systems, and site energy intensity leader for St. Charles Operations, Hahnville, La., of Union Carbide Corp., a subsidiary of The Dow Chemical Co. E-mail him at JWGathright@dow.com.