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IN THE NEWS
COST EFFECTIVE SOLUTIONS TO IMPROVE PRODUCTIVITY IN OLD ALKYD/POLYESTER RESIN MANUFACTURING PLANTS.
Published in Journal of Coatings Technology - May 2005
There are three main areas that one should investigate when considering upgrading old alkyd/polyester resin manufacturing reactors to improve productivity and reduce operating costs.
The first is Batch Time. In modern plants, typical batch times are 16-19 hours for alkyds, 14-16 hours for saturated polyesters (with phthalic anhydride feed) and 18-25 hours for saturated polyesters (with isophthalic acid feed), respectively. Of course, batch times vary somewhat from one plant to another, due to different recipes and types of operation. Generally speaking, batch times are 20 to 50% longer in old plants. This leaves a lot of room for management to spend a few dollars and justify a return on investment.
Shorter batch times mean higher production rates with the same equipment. Consequently, one must look for the obvious bottlenecks in the process such as:
a.) The raw material loading and/or product unloading steps may take too long. This can be easily fixed by retrofitting bigger equipment with proper automation.
b.) The heating and cooling transfer rates may be too slow. This is a more difficult task to tackle, since they are mainly limited by the design of the reactor and the agitator. Assuming that replacing the reactor is not a solution due to its prohibitive cost, we are left with the following alternatives.
c.) The distillation and decantation systems may be undersized. Revamping the existing equipment and adding more controls is the answer.
The second area to look at is Process Controls. It is important to examine the state of the existing instrumentation. Modern resin manufacturing plants use Programmable Control Logic (PLC) based on Human Machine Interface (HMI) control systems as a minimum, with recipe management software for the most sophisticated ones. When touring an old plant, one of the most striking points is the lack of reliable instrumentation.
For instance, monitoring product viscosity and acid/hydroxyl numbers is paramount to quality control in alkyd and polyester resin manufacturing processes. Most plants use the old-fashioned method which consists of grabbing a sample from the reactor and testing it in a lab. During this procedure, valuable time (15-30 minutes) is lost, the chemical reaction continues and the reaction end point always remains a guess.
The net result is an approximate chemical composition of the final product. To overcome this problem, some plants have installed reactor-mounted viscometers but without success. The state-of-the-art solution is to retrofit continuous on-line viscosity and acid/hydroxy number measurement systems. Such systems are proven, reliable and give instantaneous measurements of these key parameters. The operator knows the state of the reaction and the product characteristics at anytime during the batch process. The signals sent by the instruments can be integrated to the existing process control system. The benefits are numerous: (1) consistent, on-spec product, 2) slightly shorter batch time, (3) less labor involvement, and (4) safer procedure.
The third area is Energy Conservation. In the area of energy savings, all of the above mentioned improvements go a long way towards this goal. Heat and material balances can be tightly monitored with proper instrumentation. With current energy costs skyrocketing, it makes sense to retrofit mass flow meters, load cells, temperature controllers and other instruments that allow the operator to optimize the batch reaction and therefore reduce specific energy consumption.
Each plant is different, and only a complete technical audit of the existing equipment and a thorough review of the process procedures by experts will determine which cost effective solutions are the best to improve productivity.
