The Crude Distillation Unit, capacity 40,000 barrels per day, had two fired heaters with refractory-lined steel chimneys. There were dampers to control the draft at the flue gas outlets from the heaters. These were operated as a set and positioned manually, using chain wheels. The hollowed-out cast-alloy dampers (high chrome nickel steel) were 51/2' long, 24" wide, and 5" thick, weighing about 350 lbs. each. A longitudinal section showing the dampers in an open position, and cross sections in closed and open positions, can be seen in Figure 42.1. The bearing assembly details are in Figure 42.2.

Figure 42.1: Old Design of Dampers

Figure 42.2: Old Design Bearing and Pulley Arrangement

These dampers had a long history of failures. Usually, they would get stuck in one or the other position within a few days after replacement. Once this happened, they could not be rotated, making the heater draft control very difficult. The problem was known for more than ten years and there had been several unsuccessful attempts to resolve it.