Startup Procedures

Test run steps can frequently be incorporated into process startup procedures. Two examples would be pulling a vacuum on vessels and verifying it holds, or distilling a solvent and checking for the presence of water to verify the mechanical integrity of the heating and cooling equipment. 

For new processes, the employer will find a PHA helpful in improving the design and construction of the process from a reliability and quality point of view. The safe operation of the new process is enhanced by making use of the PHA recommendations before final installations are completed. P IDs should be completed, the operating procedures in place, and the operating staff trained to run the process, before startup. The initial startup procedures and normal operating procedures must be fully evaluated as part of the prestartup review to ensure a safe transfer into the normal operating mode. 

The graphioal output from the computer shows the process flowsheet, with several separation units and projeoted equipment and operating costs. It also flags information that is uncertain because it had to use thermodynamio data extrapolated from measured values. At the engineer s request, the oomputer shows several alternative flowsheets it had considered, indicates their projected costs, and tells why it eliminated eaoh of them. Some of the flowsheets were eliminated because of high cost, others beoause they were oonsidered unsafe, others because the startup procedures would be difficult, and still others because they were based on uncertain extrapolation of experimental data. 

Another important consideration regarding the character of constraints, h,, is their hierarchical articulation at multiple lerels of detail. For example, suppose that one is planning the routine startup procedure for a chemical plant. Safety considerations impose the following constraint on the temporal ordering of operations ... 

In order that different perspectives may be applied, members from research, process engineering, project engineering, construction, and production should be at the review meeting. Notes should be taken at this meeting on how to shut down the plant under any set of circumstances. Startup procedures should also be documented to see that they can be done easily and safely. It is reviews like this that help prevent the multimillion-dollar fires and explosions that have destroyed many plants and taken many lives in recent years. 

Here are some additional remarks on the startup procedure ... 

An air pocket in the pump can cause low or no pressure or flow, erratic pressure, and changes in retention time data. It may be necessary to bleed air from the pump or prime the pump according to system startup procedures. Air pockets in the column will mean decreased contact with the stationary phase and thus shorter retention times and decreased resolution. Tailing and peak splitting on the chromatogram may also occur due to air in the column. Air bubbles in the detector flow cell are usually manifested on... 

The material of construction for the screw is critical in order to provide the proper strength in the event of an improper startup procedure such as a cold start and to minimize cost. The choice of the material of construction depends on the motor size, the maximum screw speed at the base motor speed, and the depth of the feed section. The maximum torque that the motor and gearbox combination can supply to the screw, (Nm) is computed as follows ... 

Whenever multiple steady states in a reactor are possible, we must be very concerned that we are operating on the desired steady-state branch. This requires a proper startup procedure to attain the desired steady state and suitable operation limits to make sure that we never exhibit a sufficiently large transient to cause the system to fall off the desired conversion branch. We will consider transients in the CSTR in the next section. 

Does the cleaning procedure or startup procedure ensure... 

Once the actual extraction-section aqueous feed is started, the process should be close to steady state after three residence times of the fluid have passed through the contactor stages. This action will typically take 15 to 30 min. If the above startup procedure is used, the decontamination factor for the extraction section will always be greater than the desired value, even during startup. Once steady-state operation is reached, the process is easy to control. The operator needs to check that the required feed flow rates are maintained, that the feed in each feed tank is appropriate, and that the rotors are spinning at the proper speed. Also, the feed tanks need to be monitored to avoid them running dry, and the effluent tanks need to be monitored for overflow. In plant operation, these tasks are usually automated. 

Whereas the operation of batch reactors is intrinsically unsteady, the continuous reactors, as any open system, allow for at least one reacting steady-state. Thus, the control problem consists in approaching the design steady-state with a proper startup procedure and in maintaining it, irrespective of the unavoidable changes in the operating conditions (typically, flow rate and composition of the feed streams) and/or of the possible failures of the control devices. When the reaction scheme is complex enough, the continuous reactors behave as a nonlinear dynamic system and show a complex dynamic behavior. In particular, the steady-state operation can be hindered by limit cycles, which can result in a marked decrease of the reactor performance. The analysis of the above problem is outside the purpose of the present text ... 

The reactor is characterized by no addition of reactant or removal of product during the reaction. Any reaction being carried out with this constraint, regardless of any other reactor characteristic, is considered batch. The assumptions for batch operation are (1) the contents of the tank are well mixed, (2) reaction does not occur to any appreciable degree until filling and startup procedures are complete, and (3) the reaction stops when quenched or emptied. The reactor can be operated with either a homogeneous or heterogeneous reaction mixture for almost any type of reaction. 

Several local newspaper articles explained that during these startups, steam is provided to displace any air in the system prior to the introduction of any oil. At the beginning of the startup, temperatures in the unit are cool enough to condense some of the steam into water. Water (steam condensate) collects in the E-l Fractinator and then is pumped into another part of the unit, the F-7 Drum. Under normal startup procedures the operating crew drain all of the water from the F-7 Drum before the hot oil is admitted. 

What if improper or inadequate startup procedures are written ... 

The dynamic model proposed proved to represent well the separation in a DWC of a ternary hydrocarbon mixture. The values of internal flows and temperature distributions along the trays reached at steady state were in good agreement with the simulations obtained in the frame of commercial simulators. The use as control variables the reflux ratio or the side-stream flowrate proved to enable a reduction of the startup time with about 70 % compared with classical startup procedures. The complex technique developed can be a useful tool in studying dynamic behavior and startup optimization for complex columns and can be easily extended to various mixtures. 

The following are the pre-startup procedures (a) Check operation of the chlorine pressure reducing valve (PRV) by turning ON the power switch on the sludge oxidation unit control panel. Turn the chlorine valve switch to the OPEN position, observe operation of valve actuator (b) turn switch to the CLOSED position and (c) adjust time delay relays according to the manufacturer s instruction manual. 

Branch judiciously. References should not be used to make the writer s life easier. Sending the user to other procedures or documents may make writing the procedure easier, but it makes the procedure very cumbersome. Operators and mechanics often complain that the number of references in a procedure is so great that it makes the procedure impossible to use. For example, a startup procedure refers to a compressor startup procedure which in turn refers to a turbine startup procedure, and so on. If you are just using a step or two from another procedure, copy the step to the procedure you are writing. 

Development of the MTG startup procedure was carried out with extensive use of steady state simulation models. 

Detailed sensitivity analyses were implemented on various sections of the plant to provide guidelines for operation. The MTG unit startup procedures were developed using multiple quasi-steady state steps. Follow-on work involved development of plant optimisation techniques and further expansion studies. 

This section covers melt temperature and profile, screw rotation, injection speed and pressure, mold temperature and back pressure, cycle management, clean-out procedure, and shutdown and startup procedures. 

Instrumentation and automatic control is desirable in plants of this size to allow for automatic shutdown and alarm in case events should occur during unattended periods which might be deleterious to the plant or the product water. Automatic startup, however, is not a requirement if there is adequate product water storage, if the startup procedure for the plant can be carried out in a short time, and if an operator is available on call. 

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