Conco service technicians have cleaned more than 100 million heat exchanger and condenser tubes at industrial and power generation plants. Our effort to bring Conco technology to more industrial venues has brought to light the need to provide maintenance to the plant Sulfur Recovery Unit (SRU), a component as prone to fouling as the heat exchanger and condenser.
The SRU is extremely important in many industrial settings including oil refining and gas processing plants. Hydrogen sulfide (H25) is a by-product of high-sulfur crude oil and natural gas processing, and is a very toxic gas at high concentrations. Because hydrogen sulfide is defined as both an environmental and industrial pollutant, plants are required to recover between 95 ad 99.9 percent of total sulfur that arrives at the SRU. The SRU converts hydrogen sulfide to nontoxic elemental sulfur. Without the SRU, the toxicological and environmental consequences of H25 would be harsh and severe, including acid rain and ground level sulfur dioxide contamination. Because the stakes are so high for refineries and other plants that must manage H25, the SRU must be well maintained, reliable and able to meet the required recovery efficiency for the long term.
The proper performance of SRUs within a process can affect the cost of the final product, or even the production rate. Unfortunately, SRUs are prone to fouling, its nature depending on the fluids flowing within and over the tubes: and the reduction in heat transfer that results almost invariably has an impact on product cost. To reduce this impact, SRU performance should be intelligently monitored and the SRU cleaned at intervals that are determined from optimal economic criteria.
Sulfur Recovery Unit Fouling and its Effects
The fouling that occurs within an SRU is usually not due to a single mechanism, although sometimes one mechanism will be dominant. Fouling tends to increase over time, with the trajectory being very site specific. Fouling has an economic impact, and determining when to clean often requires striking a balance between maximizing the quantity of the finished industrial product from the process and its cost. The sulfur buildup that accumulates in the tubes of SRUs can be hard and chalky, and it is not uncommon for tubes to be wholly obstructed with fouling.
Sulfur Recovery Units are a part of a process and when fouling occurs, the temperature of the heating fluid must rise if the same amount of heat is to be transferred through the tubes. This temperature rise must be associated either with an increase in the total energy input to the process or a reduction in production rate, both of which represent a cost incurred due to fouling. Clearly, in order to make intelligent economic decisions, these costs must be quantified at a series of points in time and, preferably in relation to the fouling resistance as well.
Methods for Cleaning the Sulfur Recovery Unit
- TruFit® Tube Cleaners
- Liquid Nitrogen
- HydroDrill™
To improve the performance of fouled SRUs requires that the tubes be cleaned periodically. Each time the tube deposits are removed, the tube surfaces are returned almost to bare metal, providing the tube itself a new life cycle.
TruFit® Mechanical Tube Cleaning
The most frequently chosen and fastest method to address light to moderate SRU fouling is the TruFit mechanical tube cleaners. The TruFit system is an offline method in which the mechanical tube cleaner is propelled through the tube with low-pressure water, flushing the debris out of the tube, leaving the tube free and clear of fouling. Figure 1.0 shows a mechanical tube cleaner in action. For off-line mechanical cleaning it is essential to select the appropriate cleaner. The TruFit cleaner manufactured by Conco has proven to be the most effective.
HydroDrill™
Sulfur Recovery Units with more moderate to heavy fouling scenarios have been successfully cleaned with the Conco HydroDrill system. The HydroDrill uses a brush or drill bit mounted to the tip of a rotating extension or Kelly Rod, and as the rod rotates, the unit pumps water through the rod to the weep holes, flushing away hardened deposits as they are loosened. Figure 2.0 illustrates the action of the HydroDrill.
HydroDrill cleaning is safe for all tube materials. Drill bits are sized to be 0.005” below the minimum tube I.D., and they feature long shanks to ensure that the axis of the bit and the axis of the tube are in complete alignment. The bits are designed with carbide tips on the leading edge only and with rounded corners to ensure that no sharp edges directly impact the tube wall. The small onsite footprint of the cleaning system, (50 to 100 sq. ft.), makes it an attractive and workable proposition.
Nitrolance™ Liquid Nitrogen Cleaning
When SRU fouling is heavy to severe, and tubes are filled and obstructed with deposition, Nitrolance liquid nitrogen cleaning can be used to restore flow. Using the power of liquid nitrogen, the super-cooled cryogenic jet emerges from the nozzle, filling cracks and crevices, expanding within the deposit, and causing rapid breakup of all debris within the tube. Figure 3.0 demonstrates the mechanics of the Nitrolance nozzle.
Liquid nitrogen cleaning is safe and ideally suited for the most challenging fouling scenarios, yielding quicker turnarounds for critical path components. And because liquid nitrogen readily dissipates, only the removed deposit is left behind, saving the plant thousands of dollars in cleanup costs. The residual sulfur deposition can be vacuumed away, leaving the SRU in as-new condition.
Maintenance for Life
There has never been a better time to consider maintenance options for the Sulfur Recovery Unit. These units are prone to fouling, but with routine assessments and periodic cleaning interventions, the SRU can maintain its reliability and efficiency for the long-term. There is a cleaning protocol for every fouling scenario and all are safe and effective.
For more information, please visit http://conco.net/ or call Conco Industrial Systems at 1-800-345-3476.