A new headered waterwall boiler configuration from RENTECH Boiler Services for this client addressed multiple issues, including emissions and continuing maintenance costs. The client, one of the largest chemical companies in the world, contracted with RENTECH Boiler Services for redesign, retrofit and upgrade of a boiler at a petro-chemical plant in southeast Texas.
The client’s wasteheat boiler produced steam using a gas turbine and auxiliary plant gas to make 235,000 PPH @ 760°F. The client’s problems included (1) furnace gases going through original furnace tube design and (2) years of replacement of refractory and ceramic tile insulation along with outer steel-welded casing. The client tried several remedies to keep furnace gases from escaping to the atmosphere, but had not prevented the furnace refractory and insulation seals and boiler outer envelope from emitting these gases.
RENTECH built a headered waterwall configuration for the boiler furnace and boiler side walls to incorporate the entire boiler in a welded headered membrane waterwall format. All furnace gases were contained within the boiler envelope without gases escaping.
The existing superheater was replaced, the unit was designed to be drainable, and tube material was upgraded. RENTECH replaced the 24 plugged tubes with new finned tubes of the original design in a repair of the convection section.
Exterior walls utilized an older design of tangent boiler tubes, which RENTECH replaced with its headered waterwall design. The new design offered a completely welded exterior wall that eliminated the expansion joint and refractory seals that eventually crack. In each RENTECH inspection of the existing boiler, flue gas leaks were present, reducing the efficiency of the boiler and creating a personnel hazard. Through age, startup and shutdown cycles, and load fluctuations, these tubes warp to allow increasing leaks of flue gas.
RENTECH minimized the amount of refractory in the boiler furnace and eliminated other types of insulation and hard steel casing. Insulation outside the membrane walls was reduced from 12-inch thickness to 4-inch thickness with corrugated lagging.