Q: We have an old alkyd and polyester resin manufacturing plant and want to increase productivity. Can you suggest some cost-effective ways to do it?

A: Productivity, when measured as the annual production of a given plant, is a key factor in assessing manufacturing costs. It is not surprising that many alkyd and polyester resin manufacturers under competitive pressures want to improve the productivity of their existing equipment at minimum cost.

The first area to look at 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 formulations and types of operations. Generally speaking, batch times are 20% to 50% longer in older 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 using the same equipment. Consequently, one must look for the obvious bottlenecks in the process, such as those noted below.

  • The raw material loading and/or product unloading steps may take too long. This can easily be fixed by retrofitting larger equipment with proper automation.
  • The heating and cooling transfer rates may be too slow. This is a more difficult task to tackle, since they are limited mainly 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.
    1. Retrofitting a new agitator that can provide gentle but more efficient horizontal and vertical mixing.
    2. Modifying the existing heating/ cooling system to provide better control of the heating/cooling rates, thus minimizing potential fouling or degradation of the product and accelerating the energy transfer.
  • The distillation and decantation systems may be improperly designed or undersized. Revamping the existing equipment, adding more controls or operating the distillation column under vacuum may be the answer.
  • The next area to look at is process controls. It is important to examine the state of the existing instrumentation. Modern resin manufacturing plants use Programmable Logic Control (PLC)-based control systems with Human Machine Interface (HMI) as a minimum; the more sophisticated systems also have recipe management software. When touring an older plant, one of the most striking points is the lack of reliable instrumentation. Adding computers and basic instruments, such as mass flow meters, load cells, temperature transmitters etc., is a relatively inexpensive solution to the problem.

    Monitoring product viscosity and acid/hydroxyl numbers is paramount to good quality control in alkyd and polyester resin manufacturing processes. Most plants use the old-fashioned method, which consists of taking a sample from the reactor and testing it in the lab. During this procedure, valuable time (typically 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 much success. The state-of-the-art solution is to retrofit continuous in-line viscosity and acid/hydroxyl 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 any given time during the batch process. The signals sent by the instruments can be integrated to the existing process control system. The benefits are numerous: consistent, on-spec product; shorter batch time; less labor involvement and a safer procedure.

    Each plant is different, and only a complete technical audit of the existing equipment and a thorough review of the operating procedures by experts will determine which of these cost-effective solutions is the best to improve productivity.

    For more information, e-mail Bernard Seguy, RHE America, at info@rhe-america.com.