Document ID: EPA-HQ-OAR-2019-0178-0021
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2019-12-12T05:00Z

THIS DOCUMENT IS DRAFT
Date:		31 October 2019
To: 		Jonathan Witt, U.S Environmental Protection Agency
From:		Bea Jackson, RTI International
		Karen Schaffner
		
Contact:	David Howe
		Cosmed Group
		https://www.cosmedgroup.com/

 Participants

Cosmed Group
David Howe, Chief Operating Officer
Christine Render, Director of Corporate Quality

U.S. Environmental Protection Agency
Jonathan Witt, Fuels and Incineration Group
Ned Shappley
Margaret Sieffert, Region 5
Tess Petesch

RTI International 
Beatrix Jackson
Karen Schaffner

 Discussion

On October 31, 2019, representatives of the U.S. Environmental Protection Agency (EPA) and their contractor (RTI International) participated in a meeting with representatives of Cosmed Group (Cosmed).  Mr. David Howe of Cosmed began the discussion with an overview of scrubber categories and the development history of the Glygen air pollution control device.  

Glygen Units Overview

Mr. Howe explained that Cosmed has built and used Glygen units since the early 1990s. There are many different types of liquid acid scrubber designs.  He noted that packed bed towers are a common wet acid scrubber design used in the ethylene oxide (EtO) commercial sterilization industry.  In a packed bed tower, there is a column of packing material, the acid water solution is introduced at the top of the column, and the gas flow from the process is introduced at the bottom of the column.  The gas and liquid interface over the bed packing material as each flows countercurrently through the column.  The Glygen unit is not a packed bed tower design but rather the Glygen refers to a bubbling technology where the gas stream is bubbled through a tank of acid water solution.

Cosmed roughly based the Glygen unit design on an older scrubber design and improved it for EtO control.  (The older scrubber was Damas wet scrubber technology.) The Glygen unit consists of a "liquid scrubber," commonly referred to as a reactor tank or scrubber tank, filled with water and sulfuric acid (H2SO4) solution, with a diffusion plate at the bottom of the tank, and the gas flow from the process is introduced at the bottom of the tank.  The diffusion plate at the bottom of the scrubber tank is a stainless-steel plate perforated with thousands of small laser-cut holes.  The gas stream from the process bubbles through the diffusion plate into contact with the acid water solution, and the EtO is absorbed into the solution, resulting in efficient EtO removal. All Glygen units use H2SO4 solution to create a low pH solution in the scrubber tank to catalyze the reaction of EtO to ethylene glycol (EG).

Mr. Howe explained that the Glygen unit is a two-stage unit that is designed with two scrubber tanks operating in series.  This ensures small bubble size in each tank, i.e., that there is sufficient exposure area with the acid water solution; when the gas bubbles are larger in size, this reduces the EtO removal efficiency. 

Mr. Howe further stated that the Glygen unit operates at relatively low pressure, i.e., less than 5 pounds per square inch (psi).  The pressure from the vacuum pump provides the force to move the EtO process stream through the scrubber tanks. 

The Glygen units are designed for use on process units that have high EtO concentration and low gas flow rate.  The emission points most commonly controlled include the sterilizer chamber vent (SCV) and sometimes the chamber exhaust vent (CEV) can be controlled as well.  The Glygen is not typically used for low EtO concentration and high flow rate streams, such as would be typical for an aeration room vent (ARV) or room area air.  High flow rates tend to lower the destruction and removal efficiency (DRE) of the Glygen unit.  Better contact between the gas and the acid water solution is achieved with lower gas stream flow rate and higher liquid volume. Mr. Howe emphasized that lower flow rates generate higher efficiencies, resulting in less gas passing through higher volumes of water. 

Since 2004, Cosmed has often paired Glygen units with packed bed towers.  The ARVs are often vented to the packed bed tower, if these are in place. Mr. Howe noted that the Glygen application is not patented. 

In the original Glygen design, units consisted of a reactor tank, a bubbling tank, and a liquid pump between the two tanks that recirculated the acid water solution. If the pump between the two tanks was not working correctly, the DRE was affected. Cosmed later redesigned the Glygen to avoid any moving mechanical parts.  Use of the new design with scrubber tanks with no circulation of the acid water solution made the volume of the Glygen much larger.  Although larger, the Glygen design with no moving parts is simple and durable/reliable.  The older Damas scrubber unit used tubes made of sintered material that each handled 1 cubic feet per minute (cfm) of gas flowrate.  As mentioned previously, one of the improvements over the Damas scrubber is that the Glygen unit uses a laser cut plate in the bottom rather than the tubes.

Initially, Glygen scrubber tanks were made of polyvinyl chloride (PVC) material, however, these were subject to cracking over time. Cosmed revised the material to stainless steel, and stainless steel tanks are now in use. 

Cosmed is not aware of the use of Glygen units in other industry sectors.

Sterilizer Chamber Operation

Cosmed has added combination sterilizers, i.e., all-in-one sterilizers, that conduct both sterilization and aeration operations in the same sterilizer unit.   In the last 5 years, approximately 50 percent of Cosmed facilities operate combination sterilizers, and the other 50 percent operate with a more typical sterilization process with a sterilizer chamber followed by a separate aeration unit. Cosmed noted that the majority of typical sterilizers have the capacity to operate as all-in-one units, simply by increasing the number of washes following the sterilization step and to continue to aerate within the sterilizer chamber. 

The Glygen unit can be applied to a wide range of products.  As a contract sterilizer, Cosmed handles most every type of product and is able to handle products with different residual EtO standards. In general, the industry tendency is toward longer sterilization cycles and longer aeration.  When a combination sterilizer chamber is used, the product remains in the chamber for a longer period.  This combination sterilizer approach results in a reduction of EtO emissions in comparison to those with separate aeration rooms. When product is removed from the sterilizer chamber for placement in a separate aeration unit, the offgassing of EtO results in dilute EtO concentrations in the room area air that are more difficult to control.  Containing the EtO in the sterilizer chamber equipment is best. Mr. Howe noted that there are some sensitive products for which aeration in a separate room may be necessary because the product requires slower aeration. Mr. Howe noted that the combination sterilizer approach that combines the sterilization operation and the aeration operation in the same chamber is ideal, and he indicated again that most all sterilizer chambers can adopt this approach.

Glygen Removal Efficiency 

Mr. Howe noted that the Glygen units are designed to comply with the NESHAP and often are enhanced to deliver an efficiency of 99 percent or better.  While the federal NESHAP requirement is 99 percent, multiple state regulations require more stringent control efficiencies (e.g., California requires 99.9 percent).  EPA noted that a facility in South Carolina reported achieving a 99.999 percent removal efficiency for its Glygen unit.  Mr. Howe suggested that the enhanced efficiency of 99.999 percent achieved by the South Carolina facility may be in response to additional regulatory requirements by state agencies or risk assessment requirements.  Mr. Howe noted that the efficiency of the Glygen technology can be influenced by a number of variables such as gas flow rate from the sterilizer chamber (or vacuum pump system), the scrubber tank water volume, and how well the Glygen unit was sized. 

To achieve higher control efficiency, the outlet stream from the Glygen unit may be vented to a second APCD in series, e.g., a packed bed tower. Higher efficiencies may involve polishing scrubbers such as packed towers, that are highly compatible with Glygen application. If the packed bed tower achieves 99 percent control, then the overall control efficiency of the Glygen unit followed in series with the packed bed tower is greater than 99 percent.  The packed bed tower is not part of the Glygen unit, it is a second, separate control device.

Mr. Howe also explained that different types of vacuum pumps, for example liquid ring vacuum pumps and air sealed vacuum pumps, may be used for the sterilizer chambers. Glygen units with liquid seal vacuum pumps may actually achieve slightly better efficiencies because the water in the pump seal also absorbs EtO, which results in increased efficiency. 

On average, 100 gallons (gal) of acid water solution is able to absorb approximately 30 gal of EtO.  Mr. Howe stated that Glygen units achieve a DRE of greater than 99 percent, until the operating limit of the absorbing limit of the acid water solution is reached. 

Compliance testing is typically conducted at peak conditions and under worst case scenarios, for example when multiple sterilizer chambers are vented to one Glygen at once.

Monitoring Activities

Mr. Howe indicated that typical monitoring activities would include monitoring the scrubber tank solution level, testing for the EG concentration, and monitoring the pH. Glygen units are equipped with alarm systems that are activated when critical levels are reached.  The scrubber tanks are often equipped with high and low alarms, and the alarms are triggered before the tank level reaches its maximum, i.e., several inches below.  Operators monitor the tank levels daily.

The Glygen scrubber tanks are replenished periodically in "batch" mode, i.e., all acid water solution is removed at one time. When maximum EG concentration or scrubber tank level is reached, the acid water solution and the EG in the scrubber tank are removed, and the empty tank is replenished with new acid water solution and the scrubber tank is ready to go back online. The acid water solution and EG are not removed until the maximum level is reached.  The solution in the scrubber tank is moved to an EG storage tank.  The EG storage tanks are typically vented to the packed bed tower or to a catalytic oxidizer.  The replenishment of the Glygen scrubber tank occurs when the sterilizer chamber is not in operation. 

There are no mechanical parts in a Glygen unit that require monitoring, therefore major maintenance downtime does not occur. Mr. Howe stated that in most cases, facilities have daily or weekly inspections of the control device. 

Monitoring for a packed tower scrubber is typically done at the scrubber liquid recirculation tank.  The circulating acid water solution is collected in the recirculation tank and returned to the top of the packed bed column.  Periodically, the acid water solution is moved from the recirculating tank and collected in the storage tank. 

Capital and Annual Costs

Mr. Howe shared capital and installation cost data for the largest size sterilizer chamber that Cosmed uses.  The Total Capital Investment for a Glygen unit would range from $150,000 to $200,000 for venting of either one large sterilizer chamber that can handle a tractor trailer size load of product (i.e., a set up with one sterilizer chamber to one Glygen unit), or for venting of four sterilizer chambers that are "6-pallet" chambers (i.e., a set up with four sterilizers to one Glygen unit).  The cost cited is based on stainless steel materials for the tanks.

The gas flow rate from the process largely depends on the size of the sterilizer chamber. For a set up of one large sterilizer chamber and one vacuum pump that are sized to handle a load of product equivalent to a tractor trailer, the flowrate would peak at approximately 700 to 1000 cfm. In a different setup, where several sterilizer chambers, each with a volume sufficient to handle the product load equivalent to a tractor trailer, are vented to one Glygen unit, this setup would roughly double the peak flowrate to approximately 2000 cfm. One-to-one setups with one sterilizer chamber venting to one Glygen unit are more common, because these units can undergo initial testing without affecting other existing operations. 

Operating costs for the Glygen unit include water usage, electricity, H2SO4 usage, sodium hydroxide (NaOH) usage, and the dumping/disposal cost for EG. 

Mr. Howe reviewed an annual cost example for one Glygen unit controlling a 30-pallet sterilizer chamber operating at maximum capacity.  The Glygen unit is a two-stage system where each stage has equivalent absorption capacity.  The first, primary scrubber tank absorbs the most EtO and gets replenished more often than the second scrubber tank. The primary scrubber tank would be replenished approximately once every 2 (1/2) weeks with approximately 1000 gal of water. The second scrubber tank typically needs to be replenished approximately once per month with 1000 gal of water. Mr. Howe estimated that a large Glygen unit would need a total of approximately 40 to 50 water replenishments per year, for a total of approximately 50,000 gallons per year (gal/yr). 

In addition to the water replenishment, a 50 percent H2SO4 solution is added to the water. The annual usage of H2SO4 solution is approximately 1,200 gal/yr. Approximately 4 gal of 60 percent NaOH solution is used at each replenishment for neutralizing the spent acid water solution and EG, and approximately 200 gal/yr is used. Some of the spent acid water solution and EG is recycled/used and some is waste.

Minimal maintenance is needed for the Glygen unit.  There is minimal component replacement since there are no moving equipment parts, and there is no fouling of equipment due to stainless steel material.  The Glygen unit does not need to be taken offline for any significant length of time for maintenance activities. In comparison, if the Glygen is paired with a packed bed tower, the packed bed tower would have to come offline for maintenance and there would be downtime for replacing the packing.

With respect to the APCD lifetime, Mr. Howe noted that the equipment lifetime is roughly 25 years, if the scrubber tank material is stainless steel.  He noted there are older Glygen units that are still operating that are between 25 and 30 years old.

Closing

In closing, Mr. Howe offered to answer any additional questions EPA or RTI may have on the Glygen unit in the future.  Mr. Howe noted that Glygen units operate really well, and that an add-on packed bed tower can be added to increase the emission reduction, this is not difficult to do.