Off-specification products

For most processes, the optimum operating point is determined by a constraint. The constraint might be a product specification (a product stream can contain no more than 2 percent ethane) violation of this constraint causes off-specification product. The constraint might be an equipment hmit (vessel pressure rating is 300 psig) violation of this constraint causes the equipment protection mechanism (pressure relief device) to activate. As the penalties are serious, violation of such constraints must be very infrequent. 

Discussion with operators provide substantial insight. The purpose of the discussion should be to develop an understanding of operators perspec tives of the unit, their foci for the operation, and their decision sequence in response to deviations and off-specification products. Two additional, albeit nontechnical, goals of this discussion are to establish rapport with the operators and to learn their language. The operators will ultimately be required to implement recommendations developed by analysts. Their confidence is essential to increase the likehhood of success. The following topics should be included in the discussion. 

Chemicals may be encountered as reactants, solvents, catalysts, inhibitors, as starting materials, finished products, by-products, contaminants, or off-specification products. They may vary from pure, single substances to complex proprietary formulations. 

Obtain all available information about the material. If it is a surplus or off-specification product, obtain an analysis or a Material Safety Data Sheet. If it is a waste, check for previous analyses, and if none exists, obtain one. (Even if a previous analysis exists, consider running a few screening-type field analyses for confirmation of important properties such as pH, redox potential, or other oxidizer test such as cyanide, sulfide, and flashpoint.)... 

Off-specification products during startup, shutdown or plant upsets. Means of disposal of all off-specification product streams must be available. In many cases, blending off in product tankage or downgrading of another product is possible. 

The Chemical Process Industry (CPI) uses various quantitative and qualitative techniques to assess the reliability and risk of process equipment, process systems, and chemical manufacturing operations. These techniques identify the interactions of equipment, systems, and persons that have potentially undesirable consequences. In the case of reliability analyses, the undesirable consequences (e.g., plant shutdown, excessive downtime, or production of off-specification product) are those incidents which reduce system profitability through loss of production and increased maintenance costs. In the case of risk analyses, the primary concerns are human injuries, environmental impacts, and system damage caused by occurrence of fires, explosions, toxic material releases, and related hazards. Quantification of risk in terms of the severity of the consequences and the likelihood of occurrence provides the manager of the system with an important decisionmaking tool. By using the results of a quantitative risk analysis, we are better able to answer such questions as, Which of several candidate systems poses the least risk Are risk reduction modifications necessary and What modifications would be most effective in reducing risk ... 

Unused reactants can be recycled and off-specification product reprocessed. Integrated processes can be selected the waste from one process becoming the raw material for another. For example, the otherwise waste hydrogen chloride produced in a chlorination process can be used for chlorination using a different reaction as in the balanced, chlorination-oxyhydrochlorination process for vinyl chloride production. It may be... 

Foreign material contamination in a resin feedstock can destroy value to the processor by the production of off-specification product and by shutting down a line due to the formation of holes in a product web or a hole in a blown film bubble. To mitigate the economic loss, the processor must be able to identify the contaminant quickly so as to minimize the level of off-specification product. Moreover, the off-specification product needs to be isolated before a decision can be made to either... 

Outdoor storage related to processing facilities can encompass a wide-range of chemicals including raw materials, intermediates, finished, and off-specification product in a variety of container types such as drums, portable and tote tanks, and intermodal tank containers. Materials, including spare, surplus, or salvaged equipment, are also stored outdoors. 

Hazardous waste may be a listed discarded chemical, an off-specification product, an accidental release, or a liquid or solid residue from an operation process, which has one or more of the characteristics below ... 

Often may be assumed a capitalistic euphemism for Safety The Journal of Loss Prevention in the Process Industries, or the proceedings of the eponymous annual, conference will be found to concern themselves almost entirely with averting potentially deadly mishap - which will also be destructive of equipment. Little if any attention is given to avoiding the production of off-specification product, a regular and large loss to industry. 

The economics of most processes are determined by the steady-state operating conditions. Excursions from these steady-state conditions usually have a less important effect on the economics of the process, except when the excursions lead to off-specification products. To enhance the economic performance of a process, the steady-state operating conditions must be altered in a manner that leads to more efficient process operation. 

In a few applications, improving the control system leads to a reduction in off-specification product and thus improved process economics. However, in most situations, the process is operated sufficiently far from the constraint that very little, if any, off-specification product results from control system deficiencies. Management often places considerable emphasis on avoiding off-specification production, so consequently the target is actually set far more conservatively than it should be. 

Process actions. These are designed to prevent process conditions that would unduly stress equipment (perhaps leading to minor damage), lead to off-specification product, and so on. Basically, the process actions address hazards whose consequences essentially lead to a monetary loss, possibly even a short plant shutdown. Although sometimes referred to as interlocks, process actions address situations that are not deemed to be process hazards. 

Normal Consequences—Class 3- Instrument systems that are used to alert the chemical process operator of a nonhazardous abnormal condition that might otherwise be undetected. The failure to react to one of these alarms may create an off-specification product such as a low temperature alarm on certain distillation columns. These systems are not included in the prooftest program. 

In CBD operation (Figure 11.1) each cut (one pass) produces either a desired product (main-cut) or an off-specification product (off-cut). The recovery of key component in each cut can be maximised by controlling reflux ratio optimally and by having a number of time sequenced reflux ratio (Chapter 5, 6). The process... 

When a number of products are produced sequentially using one pass to produce one distillate product from a binary or a multicomponent mixture in a continuous column, the operation is defined as SPSSS operation. For binary mixtures there will be a maximum of two distillate cuts, one being a specified product cut and the other being an off-specification product cut. Under such condition, of course, the final bottom product will be of specified purity. Figure 11.4 illustrates the operation for a ternary mixture. Here two passes are allowed in the same column sequentially. The first pass separates component A and the second pass separates component B. 

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