Plant startup phases

Modern nitric acid plants are designed for energy self-sufficiency during normal operation. Except for the startup phase, process heat generated will equal energy consumed by the compressors. Moreover, in many cases surplus energy can be exported in the form of steam, for example. 

Starting up the turbocompressor installation of a nitric acid plant does not present a problem. As mentioned earlier, during the startup phase the expander is not able to contribute any power. Accordingly, electric motor drivers must initially provide power in excess of the nominal operational rating. 

Smooth starts are possible with steam turbine installations that include an auxiliary boiler because the startup phases of the turbocompressor can be matched to different plant operating conditions. Aside from process-related timing issues, the time elapse or machinery startup duration is generally determined by the temperature gradients admissible on both steam turbine and expander. These factors are influenced by the relative expansion rates of the fixed and rotating components in these machines. 

The aeration requirements of the deep shaft (vertical shaft bioreactor using flotation technology) are provided by two, 100 hp rotary screw compressors rated at a pressure of 7 kg/m2 (100 psig). Dissolved oxygen (DO) levels of 4 mg/L are maintained in the head tank, and during the startup phase of the plant a DO meter measured a dissolved oxygen concentration of 25 mg/L at the shaft bottom. 

Plant startup The commercial plant is started. In this phase, no actions for process intensification studies can be defined. 

After the plant is constmcted, the operations phase of the project begins, which includes plant startup. Rarely does this operation proceed smoothly. Troubleshooting, process modifications, and repairs are generally required. 

The last, but very important, phase of a construction project is the plant startup. On a major project this is as significant an event as Front End Loading or Design Construction. 

The interaction of the plant with the research and development area will be most significant during the design and startup phase of the plant and each of its products. The regulatory activities that would be required for the preparation and filing of the required documentation for the FDA, in the United States, or the Health Ministry of the country where sales are planned will be the subjects of discussion in the appropriate chapter. 

The 4S employs a reactivity control system with an annular reflector in place of the control rods and driving mechanisms which traditionally require frequent maintenance service. Reactivity is controlled only by the vertical movement of the annular reflector during plant startup, shutdown and power generation, thus eliminating the necessity for complicated control rod operations. Although this reactivity control method using a reflector has been studied in some projects using this method for the core bum-up phase is a new approach. 

To evaluate the net present value (NPV) of a proposed plant, its cash flows are computed for each year of the projected life of the plant, including construction and startup phases. Tlien, given the interest rate specified by company management (typically 15%), each cash flow is discounted to its present worth. The sum of all the discounted cash flows is the net present value. The NPV provides a quantitative measure for comparing the capital required for competing processes in current terms. However, the result is usually quite sensitive to the assumed interest rate, with proposed processes changing favor as the interest rate varies. An... 

Late one night, a brand new distillation column was wrecked by vacuum and toppled as a water filled flooded column was being pumped out. The column was designed and equipped with sufficient under/over pressure protection during normal operations, but the system was ill equipped to deal with flooded columns at startup. This was a newly constmcted plant, which had been in the pre-startup phases. 

After an unexpected failure in one of the BAHX during the initial phase of the plant startup due to concluded temperature excursion and the subsequent failure analysis, new trip protection has been included in the control logics. In the analysis the main probable cause that could have occurred is the sudden vaporization of filled liquid inside the BAHX, more importance was provided to avoid liquids in the exchanger inlet by modified controls. 

J. Cai, Y. Ishiwatari, S. Bcejrri and Y. Oka, Thermal and Stability Considerations for a Supercritical Water-cooled Fast Reactor During Power-Raising Phase of Plant Startup, Proc. ICAPP09, Tokyo, Japan, May 10-15, 2009, Paper 9265 (2009)... 

Thermal and Stability Considerations During Power Raising Phase of Plant Startup... 

The power raising phase in the plant startup was designed in consideration of the thermal and thermal-hydraulic stability criteria. Due to the two-pass flow scheme, the power to flow rate ratio became locally large in the downward flow channels during certain power and flow conditions. Thus, the flow rate required to satisfy those criteria was determined by the MCST and the decay ratio of thermal-hydraulic stability in the downward flow channels. 

Mission Control will not be in direct control of each step of the startup sequence. Time delays in the communication path between Mission Control and the spacecraft preclude real time monitoring and control of plant functions. Also, continuous communication with the spacecraft is not assured during the deployment and startup phases (Level 2 Requirements are 92%). It is therefore assumed that the control architecture for the Reactor Module would be designed such that an entire series of steps or phase of the startup would be initiated by a command from Mission Control and controlled autonomously from the spacecraft. Mission Control would wait for satisfactory indications that the sequence steps had been completed before proceeding with the next phase of the sequence. How the steps in the following startup sequence would be accomplished within the respective spacecraft controllers (Reactor Module and PCAD) has not been determined. 

The person in charge of this phase of the operation is often the person designated to become the plant manager. Some companies, however, have a startup division that is placed in charge. Others contract for this function with the construction firm. In any case, the person in charge should have had prior experience with startups. 

In a plant for the continuous nitration of chlorobenzene, maloperation during startup caused the addition of substantial amounts of reactants into the reactor before effective agitation and mixing had been established. The normal reaction temperature of 60°C was rapidly exceeded by at least 60° and an explosion occurred. Subsequent investigation showed that at 80° C an explosive atmosphere was formed above the reaction mixture, and that the adiabatic vapour-phase nitration would attain a temperature of 700° C and ignite the explosive atmosphere in the reactor. See l,3-Bis(trifluoromethyl)benzene, above... 

In the long run solid catalysts are expected to be used, which would reduce the safety problems of liquid-phase alkylations. However, much further work is needed to develop such processes,7 and their introduction will be costly. The startup of a pilot plant to demonstrate a solid acid catalyst alkylation technology jointly developed by Catalytica, Conoco, and Neste Oy has been announced.307... 

The path to pollution prevention shown in Fig. 10 is applicable at all phases of a project. In most cases, the methodology has been applied at the plant level. However, the same methodology can be used when a process is first conceived in the laboratory and at periodic intervals through startup and normal plant operation. 

Are all plant/proeess operation phases defined (startup, shutdown, abort, recovery) Are operating procedures in place for the computer system ... 

Recent deals in the field of agrochemicals - mainly made between 1997 and 1999 - have demonstrated that it is financially more effective to make a large number of early corporate venture investments in high risk plant biotechnology businesses, for example, than it is to acquire a successful startup at a later phase. The price premiums that have to be paid in the later phase are much higher than the cost of placing many bets widely at an earlier stage. 

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