Chapter 14: Scrubbers

14.1. Theory and Applications

14.2. Commissioning Scrubbers

14.2.1. Functional Testing Field Tips

Key Commissioning Test Requirements

Key Preparations and Cautions

Time Required to Test

Figures

Figure 14.1: Typical Process Scrubber

 

14.1. Theory and Applications

Scrubbers are specialized exhaust systems that clean the effluent from a process prior to discharge to the atmosphere. Scrubbers are essentially air washers that use acids, caustics, filtration, and chemical reactions to neutralize harmful substances in the exhaust stream. They are common on industrial sites and are also starting to show up on some commercial, institutional, and educational projects as air quality standards continue to tighten.

The scrubber itself is usually a component of a scrubbed exhaust system and will typically be located at the termination point of the system, immediately ahead of the exhaust fans. Scrubbers consist of an enlarged section of the duct that contains the various spray trees, filtering elements, drift eliminators, containment basins, and pumping systems required to perform the process. Many scrubbers are partially filled with balls or other media designed to allow the passage of air while providing extensive surface area for the neutralizing reactions to occur.

Often, these units are located on the exterior of the building, partially for access reasons, but also because it creates less of a safety concern in dealing with some of the noxious and toxic substances used to react with the process stream and neutralize the effluent. As a result, there can be a significant number of support systems associated with their operation that can also require commissioning, including heat trace, water make-up, chemical make-up, fire and explosion protection, and waste water treatment.

Figure 14.1: Typical Process Scrubber

This scrubber is associated with a silicon wafer plant and is designed to remove Nitrous Oxide (NOx) from the exhaust coming off of certain processes in the plant. Each of the large, rectangular shaped objects is a stage in the scrubbing process. The exhaust fans associated with the system are on the elevated platform. The vertical ducts at the top of the picture are the fan discharges, which were designed to dissipate the effluent plume to atmosphere. The prevailing winds were a significant factor in their design.

14.2. Commissioning Scrubbers

The following tables outline the benefits and background information associated with testing scrubber systems. Refer to Functional Testing Basics for guidance related to all functional testing activities, regardless of the component or system being tested.

14.2.1. Functional Testing Field Tips

Key Commissioning Test Requirements

The background information for scrubber systems is very similar to the information associated with the return, relief and exhaust systems (see Chapter 13: Return, Relief and Exhaust).

In addition to the acceptance criteria listed in Chapter 13: Return, Relief and Exhaust, scrubbers can have acceptance criteria that are dictated by the Environmental Protection Agency (EPA). The system designer should be familiar with these requirements and have specified compliance in the contract documents. The designer should be able to direct you to the governing codes and standards for performance that will allow you to determine the required acceptance criteria. Generally, an owner who requires systems of this type will have someone on staff that is charged with overseeing installation and operation. This person will be a key player in any commissioning process and may be the most familiar with the specific requirements for the scrubbers on the project. In any case, it is advisable to coordinate with the local EPA office to ensure that their testing criteria and requirements are addressed, including requirements to witness the tests and their documentation requirements.

Key Preparations and Cautions

Cautions

In addition to the cautions listed in Chapter 13: Return, Relief and Exhaust, working with or around hazardous scrubbers may require special clothing and protective equipment including air quality monitors, self contained breathing apparatus, acid suits, and emergency response and confined space entry training. It may be necessary to contract with a firm specializing in this type of work.

Instrumentation Required

Scrubber testing will generally have highly specialized and customized instrumentation and coordination requirements. In the general sense, these requirements are similar to those associated with testing Smoke Control Systems described in Chapter 15, and the information presented in that section's background information table may provide some guidance in preparation of a scrubber functional test.

Time Required to Test

The testing of scrubber systems will be time and labor intensive, but will be critical to safety, environmental protection, and efficiency. Extensive coordination with the project site's environmental health and safety staff will be required to ensure that site hazard control regulations are maintained. This important process can be time consuming and should be taken into consideration when establishing budgets.