Off-spec

In a few apphcations, improving the control system leads to a reduction in orf-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 produc t results from control system deficiencies. Management often places considerable emphasis on avoiding off-spec production, so consequently the target is ac tuaUy set far more conservatively than it should be. 

The product is more likely to be on-spec the first time, thus avoiding the need to dispose of off-spec product. 

Disposal issues pertaining to unreacted batches, incomplete batches or off-spec products. 

The raw materials are off-spec resulting in generation of excessive waste products. 

Provide procedures to safely handle the unplanned waste generation and/or neutralize off-spec materials. 

Need for reworking, blending, or disposing of partially reacted or off-spec batches. 

Provide formal procedures for dealing with off-spec batches, partially reacted batches... 

Understand chemistry and potential consequences of producing off-spec prod-ucts/waste materials, etc. 

Efforts should be make to reduce the production of off-spec material... 

Invoices statement of procedure for submitting invoices Quality Control explanation of responsibilities for analysis of supplied materials, finished product, and work in progress consequences of off-spec materials procedure for rework Process Ownership specification of who owns the process, degree of liability for remediation, procedure for review and approval of process changes... 

Removal of Processed Materials Materials such as product, off-spec material inventory, retained samples, and process... 

Clean up includes identifying, gathering, storing (when appropriate), and classifying materials associated with a specific toll. Decisions can then be made as to which raw materials, intermediates, and product will be shipped back to the client or kept by the toller. Some off-spec product, retained samples, or unused intermediates may be considered waste materials at this point. Equipment clean up can be extremely important to preserving quality and process safety integrity prior to the next production run of a new product. 

Is there a documented procedure for quarantine of off-spec materials ... 

Does all rework of off-spec materials require documented Quality Assurance authorization ... 

Ethyl aluminum dichloride (EADC) is used in the rnanufacmre of certain catalysts for making LDPE. Occasionally, the batch operation involving the catalyst production results in an off-spec lot. This off-spec lot is washed from the reactor (impregantor) with water and hexane, and must be sent to a waste disposal facility. The facility treats this waste in a hydrolysis reaction (i.e., with water and mild agitation). If the reaction is exothermic, what are the potential air pollution and fire problems associated with the waste treatment ... 

Troubleshooting deals with identifying and solving problems. Problems can be immediate or long term and can be associated with off-spec products, poor efficiency, process improvements, capacity increases, or potential shutdown items. Problems can be related to management, operation, hardware and equipment, or process issues. Solutions can include improved operating procedures and training, preventative maintenance, or installation of new equipment or controls. 

The identification of plant models has traditionally been done in the open-loop mode. The desire to minimize the production of the off-spec product during an open-loop identification test and to avoid the unstable open-loop dynamics of certain systems has increased the need to develop methodologies suitable for the system identification. Open-loop identification techniques are not directly applicable to closed-loop data due to correlation between process input (i.e., controller output) and unmeasured disturbances. Based on Prediction Error Method (PEM), several closed-loop identification methods have been presented Direct, Indirect, Joint Input-Output, and Two-Step Methods. 

A 1.3 t batch of off-spec, material had been redried in a rotating double cone vacuum drier heated by steam to around 120-130°C for 23 h. It was left in the... 

The epoxy resin component is made by a 2-stage process involving reaction of l-chloro-2,3-epoxypropane (epichlorhydrin) with isocyanuric acid to give the l,3,5-tris(2-hydroxy-3-chloropropyl) derivative, which is then treated with sodium hydroxide to eliminate hydrogen chloride to form the title compound. One batch contained more than the normal amount of hydroly sable chlorine, and when excess epichlorhydrin was distilled off, the residual material decomposed with explosive violence. It was later established that the abnormal chlorine content was associated with reduced thermal stability, and criteria for hydrolysable chlorine, epoxy content and pH have been set to prevent distillation of off-spec, material. 

Water pump fails Liquid HF not vaporized, passed to fluidized bed reactor, off-spec or no product. None. 6 Consider adding a low temperature interlock on HF (N2) flow. 

At such high throughputs and large product hold-ups, these plants are required to be very robust [2], More than one year of continuous production without maintenance is expected. In addition, the process needs to be able to be restarted after power outages of some hours without the loss of further production and with minimal off-spec material. 

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