Retrofit control systems

Design considerations and costs of the catalyst, hardware, and a fume control system are direcdy proportional to the oven exhaust volume. The size of the catalyst bed often ranges from 1.0 m at 0°C and 101 kPa per 1000 m /min of exhaust, to 2 m for 1000 m /min of exhaust. Catalyst performance at a number of can plant installations has been enhanced by proper maintenance. Annual analytical measurements show reduction of solvent hydrocarbons to be in excess of 90% for 3—6 years, the equivalent of 12,000 to 30,000 operating hours. When propane was the only available fuel, the catalyst cost was recovered by fuel savings (vs thermal incineration prior to the catalyst retrofit) in two to three months. In numerous cases the fuel savings paid for the catalyst in 6 to 12 months. 

The expander retrofit required additions to the control system due to the following modifications ... 

If the DCCS is required to replace an existing control system (i.e. if the plant is being retrofitted) then the microcontrollers will normally be located in the central control room (CCR). In this case, the distribution features of the DCCS will not be fully utilised and the significance of the digital data highway (DH) will also be reduced. 

Proper machine cycle settings are also important for energy savings. The injection speed control system (available on new machines as an option or as a retrofit on old machines) optimizes the speeds available for specific time intervals. The injection high volume pump is available for a fixed time period and is then dropped out of the system. This time period should coincide with... 

One of the advantages claimed for the technology in comparison with the sponge rubber ball system, is that it requires less maintenance. A major disadvantage perhaps in some situations more than others, is the momentary interruption in flow while the flow reversal is accomplished. The disruption of steady state conditions in the plant operation may be difficult to accommodate and could have implications for product quality. The cost of the complex piping arrangements and the control system could be expensive, particularly in a retrofit... 

A MIMO control system must be configured for the retrofitted column. To compute the RGA, a linearized model, in the steady state, relates the changes in the designated outputs, T, L, and Li, to those of the manipulated variables, gi, Q2, and S ... 

The safety of a process can be achieved by inherent (internal) and external means. Inherent safety focuses on the intrinsic properties of a process and attempts to design out hazards rather than trying to control hazards through the application of external protective systems. Inherently safer processes rely on chemistry and physics (properties of materials, quantity of hazardous materials) instead of control systems (interlocks, alarms, procedures) to protect workers, property, and the environment. It would be inappropriate to talk about an inherendy safe process, as an absolute definition of safe is difficult to achieve in this context since risk cannot be reduced to zero. However, one can talk about a process or chemical being inherently safer than other(s). For instance, water can be an extremely hazardous chemical under certain conditions (e.g., floods), but in the context of a chemical process, water is an inherently safer solvent than other chemicals. Trevor Kletz has postulated some basic principles of inherent safety [79,80] that process systems engineers can follow when designing or retrofitting chemical processes. Kletz s inherent safety principles can be summarized as follows ... 

Linkins D, Lewis D, Frank R, Weiss J (1997) TVA s Kingston Unit 9 Distributed Control System (DCS) retrofit benefit documentation. TVA Technol Adv... 

The decisions involved in retrofitting projects may be of the discrete type, the continuous type, or a combination of both. An example of a discrete decision is whether to add an on-line monitoring and control system to a waste water stream The decision is a sinple yes or no. An exanple of a continuous decision is to determine what size of heat recovery system should be added to an existing process heater to inprove fuel efficiency. This type of decision would involve sizing the optimum heat exchanger, where the variable of interest (heat-exchanger area) is continuous. 

---