ABSTRACT

Any plant operation can be divided into three types of operating steps, namely, startup, production, and shutdown. Startup and shutdown operations are unsteady state and unproductive operations. Usually, production operation is carried out for 330 days a year and 35 days are left for repair and maintenance of the plant and equipment; during this period no production is carried out. After shutdown, the startup operation is carried out until continuous production is achieved. Thus, downtime between shutdown and startup operations should not exceed 35 days. Of course, these time limits vary from plant to plant. Rarely, the partial shutdown and startup operation of a plant unit may be carried out without affecting other units such that the production from the rest of the plant may continue throughout the year. At the beginning, the power plant must be started up to supply power and steam to the plant. When the power and utilities are available in full swing, next the processing plants are started up in a sequence. For example, in a refi nery, the crude distillation plant is started fi rst. When the products from this plant meet the desired specifi cations (on spec), the secondary plants, e.g., the naphtha pretreatment and reforming plants, are started up. In fact, for old plants where suffi cient storage of intermediate products is available, all the secondary plants are started up simultaneously along with the crude distillation unit. Startup of every process plant is unique, depending on the design and operating conditions of the equipment in that plant. Though it is not possible to discuss startup procedures for every plant in a refi nery or a petrochemical plant, some of the common steps will be discussed here.

As described earlier, in a power generation plant, boiler feed water (BFW) is heated up and converted to steam to drive the turbine-alternator to generate electricity. The boiler startup is a crucial step carried out by a team of experts. Initially, pumps, blowers, compressors and other rotary machines are started after acquiring the necessary power from power plants of other companies or organisations. The instrument air supply compressors are started, the instruments are checked before putting them online. Feed water is allowed to fl ow in the furnace coils of the economiser, boiler, and superheater, and circulation is established. Next, the water level in the boiler drum is monitored and controlled. Cooling water fl ow is established through the condenser. The draft fans are started next to ensure the desired draught in the fl ue gas circuit from the superheater, boiler, economiser, and then to the stack, in this order. Fuel gas lines are opened through the pilot burners of the furnace and lit up with automatic sparking. The temperature of water in the boiler rises gradually to its saturation temperature after some time. As the steam attains at its required pressure