Heater capacity expansion

In general, fired heaters are revamped for capacity expansion, process conversion changes, energy efficiency, and NO reduction. For capacity expansion revamps, the type of limitation for the revamp is usually the same as for the original design. In conversion revamps, one type of process technology is converted to another. Thus, in conversion revamps, a heater designed for one service may be used in a new service. Therefore, the type of heater limitation may be different for the new service. 

The acti tons per year of NOx induced from the No. 2 heater were actually more than the No. 1 heater because of the larger size of No. 2. This is an important factor in the NOx control strategy dealing with individual and total emissions. For this application, the NOx inductions were obtained in order to provide offsets for expansion of refinery capacity. 

The assessment first looked into the opportunities associated with design margin. By optimizing process conditions and pushing the equipment to the absolute limits, the plant could make majority of the spare capacity and push plant capacity by 10% with some minor modifications. However, beyond a 10% expansion, several major limitations were identified from detailed simulations, which included the feed heater flux limit before the main fractionator column, jet flooding limit in the main fractionation column, and reactor space velocity limit in the hydrocracking unit. 

The single pressurizer serves all four coolant loops. It serves to hold the primary circuit pressure constant and to allow for expansion and contraction of the coolant volume caused by changes of load. An electric immersion heater of 1800-kW capacity is used to raise the pressure to, and maintain it at, the required value during negative pressure surges caused by an increase in load demand. In the event of a positive surge, caused by a reduction in load demand, a spray system, fed from the cold leg of one of the reactor coolant loops, condenses steam in the pressurizer to avoid tripping the pressure relief valves with which it is fitted. 

---