Oxygen Enrichment for Claus Units Process by Linde AG

Application: Increase the capacity of Claus plants and decompose hazardous materials such as ammonia

Description: As “clean fuels” regulations become effective, refiners must recover more sulfur in their Claus plants. As a byproduct of deep desulfurization, ammonia is generated and typically must be decomposed in the Claus plant. To upgrade the sulfur recovery units (SRUs) accordingly, oxygen enrichment is an effcient and low-cost option. Oxygen enrichment can increase sulfur capacity substantially and is capable of decomposing ammonia from sour-water stripper gas very efficiently.

Oxygen addition can be done in three levels, depending on the required capacity increase:
1. Up to approximately 28% oxygen. Oxygen is simply added to the Claus furnace air. This can raise sulfur capacity by up to 35%.
2. Up to approximately 40% oxygen. The burner of the Claus furnace must be replaced. Up to 50% additional sulfur capacity can be achieved by this method.
3. Beyond 40% oxygen. The temperature in the Claus furnace is elevated so high that the product gas must be recycled to maintain emperature control. This process is expensive and, therefore, rarely applied.

Oxygen sources can be liquid oxygen tanks, onsite ASUs or pipeline supply. Oxygen consumption in Claus plants fluctuates widely in most cases; thus, tanks are the best choice due to ease of operation, flexibility and economy. For oxygen addition into the CS air duct, a number of safety rules must be observed. The oxygen metering device FLOWTRAIN contains all of the necessary safety features, including flow control, low-temperature and low-pressure alarm and switch-off, and safe standby operation. All features are connected to the Claus plants’ process control system.

An effcient mixing device ensures even oxygen distribution in the Claus air. A proprietary Claus burner was developed especially for application for air- and oxygen-enriched operations. This burner provides for a short and highly turbulent flame, which ensures good approach toward equilibrium for Claus operation and for the decomposition of ammonia.

Economics: As oxygen enrichment provides substantial additional Claus capacity, it is a low-cost alternative to building an additional Claus plant. It can save investment, manpower and maintenance. Installed cost for oxygen enrichment per level 1 is typically below $250,000. For level 2, the investment costs range from $200,000 to $500,000 and depend on the size of the Claus plant. Operating costs are varied and depend on the duration of oxygen usage. Typically, annual costs of oxygen enrichment are estimated as 10% to 40% of the operating cost for a Claus plant, providing the same additional sulfur capacity. Due to improved ammonia destruction maintenance work, as cleaning of heat exchanger tubes from ammonium salts and the respective corrosion become substantially less.

Contributor: Linde AG, Division Gas and Engineering.