Choosing an enlightened control path

The rapid development of computer technology in advanced distributed control systems (DCS) has brought a Chinese fatty alcohol process plant safely into the modern control era.

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 By Yin Zuwei, Wuxi Dong Tai Fine Chemicals Co., Ltd.

 

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uxi Dong Tai Fine Chemicals Co., Ltd., Wuxi, Chinahas the largest fatty alcohol production equipment and the most advanced technology in China. It produces 20,000 tons/year. Fatty alcohol is made from fat and oil that react with methanol and hydrogen in the production process. The reaction pressure is over 20 Mpa, and the temperature of the reaction is more than 240° C. We selected a new distributed control system (DCS) for the Natural Fatty Alcohol Project in 2003. Using a DCS system is new to everyone at the plant because previously, automation control was barely implemented in our production.

Making Fatty Alcohol
Fatty alcohol is one of the basic raw materials in surfactants. The process produces polyoxyethylene ether products when fatty alcohol reacts with epoxyethane, which then generates alcohol ether sulfate when it further reacts with sulfur trioxide and alkali. This is the most basic ingredient of activators.

Fatty alcohol is typically used in textile printing and dyeing additives, cleaning agents, and domestic products, such as body washes, shampoos, kitchen and bathroom cleaning agents, liquid detergents, fabric softeners, toothpaste vesicant, and cosmetics.

 

            FIGURE 1: FROM MANUAL TO AUTOMATED CONTROL
           

           

Producing 20,000 tons/year, Wuxi Dong Tai Fine Chemicals Co., Ltd., is the largest fatty alcohol production facility in China and now site to some of the most advanced control technology in the country.

 

All of the raw materials are natural plant oils and animal fats, such as coconut oil, palm oil, palm kernel oil, suet, lard, cottonseed oil and soybean oil. The production equipment is composed of the host equipment and the auxiliary equipment. Auxiliary equipment includes water supply, power supply, heating, compressed air and nitrogen supply, and environmental protection treatment of wastewater.

Part of the production procedures were highly labor-intensive manual operations. Previously, fatty alcohol production was controlled by DDZ-III instruments. These are joined panel instruments composed of discrete single loop controllers with analog measurements and calculations. Mainly composed of discrete transistors, the instruments have only average accuracy and a high failure rate. To install and use the automation control instrument in the explosion prevention area (area 2), safety barriers must be added.

Unfettered by Legacy
Since we were not fettered by conventions or past experience with legacy control systems, we invited system suppliers with high-quality and cost-efficient products to bid. The bids we received were all for small to medium-scale solutions, such as ABB’s S900, Honeywell’s Plantscape system from Rosemount, and MTL Open System Technologies’ (Most) Matrix system.

We selected the Most Matrix system because of our fire and explosion prevention requirements, its distributed control capabilities, and the stringent requirements of the processes’ control targets. Wonderware InTouch software was selected for the operator interface application.

The new control system is new to China. Many people were also surprised that MTL produces and sells a DCS control system in the first place. Regardless, our main consideration was the performance of the hardware and software of the system. For the hardware, we believed that the control system was essentially an industrialized computer. The rapid development occurring in the computer field, especially in semiconductor and integrated circuits technology, gave us great confidence in choosing a digital control system.

From our point of view, the more recently developed the system, the better its performance and reliability would likely be. The hybrid controller of the new system uses the latest CPU technology, making it more advanced than other systems and one of the primary reasons we chose the system’s supplier.

MTL, one of the world’s largest manufacturers of safety barriers, has an excellent reputation in the automation industry. We thought that, because the system we purchased was a new product, it would be first-class. Moreover, besides the new functionality and good brand name, the system appealed to us because of its tight integration between the safety barrier and the I/O module. The I/O modules can be installed in a Division 2 area connecting directly to an intrinsic safety (IS) instrument without additional safety barriers. For users, this characteristic means a clean structure, low maintenance and cost-efficiency. It also saves a lot of cable and wiring costs as well.

A Dramatic Choice
To us, the process of choosing the system was dramatic. At the initial stage of the Natural Fatty Alcohol Project design, we had the idea of using distributed control technology. However, we could not be sure because we wanted to implement it in an explosion-prevention, Division 2 area. Conventional design wisdom usually prompts one to choose a combination of safety barriers plus I/O modules.

At the start MTL’s sales representatives proposed a safety barrier design to us. After they became aware we wanted to use distributed control technology, they recommended the remote I/O module of the MTL 8000 series. We felt that this was a new system structure, and it could satisfy our demand for distributed control. The problem was that not only did we need I/O modules, but we also needed controllers.

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