Currently there is a lack of mobile, low-cost vaporizer systems readily available to provide CO2 gas for large scale depopulation at swine operations. To better utilize CO2 for depopulation, there is a need for a “right sized”, mobile, low-cost, easy to use vaporizer system. This system should accomplish the necessary flow rates (CFM of CO2), to meet the AVMA guidelines for a 20% CO2 displacement rate, for the most commonly available chamber sizes (e.g. dump truck box, roll off dumpsters). Ideally a “right sized” vaporizer should be portable, easy to set up, easy to use and not require many offsite resources to run. Flow rates (CFM of CO2) should be easily adjustable to match chamber volume. The vaporizers should also be built for easy external cleaning and be able to withstand commonly used disinfectants in the pork industry.
Development of a low-cost, mobile CO2 vaporization system prototype that can be used to meet the AVMA guidelines for depopulation of swine using CO2. This vaporization system should be capable of working in most areas of the contiguous United States meaning it will need to operate in temperatures ranging from -30oF to 104oF. The following criteria were to be considered while developing the prototype:
- Ease of setup and use
- Level of training
- On-site resources to operate
- Maximum chamber volume that the system can fill at the required 20% CO2 displacement rate over 5 minutes
- Ease of external cleaning and disinfection
- Cost to produce is less than $75,000 USD/unit.
Narrative on how research was conducted
A simple ambient air CO2 vaporizer was utilized as the basis of this system to keep in alignment with low cost and simplicity to operate. Ambient air vaporizers utilize the ambient conditions to increase the temperature of the CO2 to convert liquid CO2 to gaseous CO2. Liquid CO2 is not typically available on farms but can be delivered through providers such as Air Liquide or Praxair.
The first phase in the research was to engineer the system and select appropriate equipment to meet the objectives of the project. Ambient air CO2 vaporizer are designed for continuous use in a vertical orientation, typically in soda bottling facilities, applications that allows for various ranges of flow rates and ambient air conditions and the required horizontal orientation to properly fit on a trailer created challenges to source a vaporizer that would fit the application and still be able to be mounted on a trailer so it could be mobile.
Once the appropriate vaporizer was selected, the next engineering objective was to design the process to be both simple and functional. Vaporization of CO2 is dependent on both temperature and pressure of the liquid/gas; vaporization can be achieved at lower temperatures if the overall pressure is decreased. A pressure regulator was, therefore, installed upstream of the vaporizer to reduce the inlet pressure of the liquid CO2 to help achieve the desired vaporization rates at low ambient temperatures. A regulator was also installed on the outlet of the vaporizer to maintain the outlet pressure to the depopulation chamber. A simple flow meter that runs on the trailer’s 12-volt system was installed to provide real time flow rates to the operator.
Once design was completed, all necessary parts and materials were procured to build the prototype. Many of the items were long lead items as these are fairly specialized parts for this application. Once materials were received the system was constructed on a mobile flat deck trailer.
The last phase of the project was to test the system and validate any assumptions of the project. After completion of the initial testing, it was determined that the regulator located downstream of the vaporizer was insufficient to maintain pressure in the vaporizers. This resulted in dry ice formation in the system and a failure of all of the flow control equipment.
Based on this, it was determined that either a control valve or a back pressure regulator would be required to maintain a minimum of 80 PSI in the vaporizer, as lower pressures could result in dry ice formation and system failure. The manual control valve that was originally located upstream of the vaporizer was moved to a downstream location to act as the back pressure regulator since a regulator sized for this application would be price prohibitive.
The second testing event demonstrated that relocating this control valve maintained the required pressure in the vaporizer, which allowed the system to function properly. This allowed the system to be tested under the various flow rates required for the proposed depopulation chambers. Testing was completed on a relatively warm day (~80 oF) so the system will require further testing at lower ambient temperatures in the winter of 2021-2022 to determine the sizes of depopulation chamber that can be used at various low ambient temperatures.
Overall, the findings were that we were able to design, construct, and test a prototype system that met the seven requirements as listed in the summary above. The large majority of the costs of this prototype project were in the design, procurement, and testing of the system. Based on the materials and equipment selected it was determined that the system can be built for the required maximum cost of $75,000 USD as set out in the budget objectives.
Standard operating procedures (SOP’s) were developed to aid in the operation of the system and for the training of operators. To maintain a low cost and simple operation, the system is controlled and operated manually by valves, therefore training and operation are very simple. The entire system is mounted on an 18 foot flat deck trailer that can be pulled by a 3/4 ton or larger truck making it a very mobile system.
The vaporizer, piping, valves, and exterior equipment components are either aluminum or stainless steel that are suitable for outdoor use and storage, and cleaning with most industry standard cleaning products (Extreme bioshield, bleach, or hydrated lime should not be used on the equipment).
The system was designed with flow control to ensure flowrates and distribution pressures are sufficient for depopulation purposes, while not causing undue stress on the livestock. CO2 flow rates will be monitored by an operator to ensure proper delivery rates are achieved based on the depopulation chamber size. The SOP includes a table that provides the conversion of cubic feet per minute (CFM) required for each standard depopulation chamber to standard cubic feet per hour (SCFH) that is read on the flow meter display. This will allow operators to ensure the proper volumes are provided based on the ambient temperature during depopulation events.
The system can be run by two people: one that operates the control valve and maintain the flow rate, the other to hook up/unhook the hose to the depopulation chamber.
- Simple, easy to operate system (No complex boiler, heating systems or electrical systems)
- Portable, weighs less than 4,550 lbs. (Can be towed behind 3/4 ton or larger trucks)
- Cost-effective (Post prototype systems can be built for $75,000 USD)
- Flexible for various depopulation chamber sizes (The vaporizers are capable of providing a large flow rate for depopulation chambers in excess of 3,000 ft3)
- Can be cleaned and disinfected by most industry-standard cleaning agents