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When the Wilkinson County Correctional Facility was notified that its natural gas line was being decommissioned, warden Jody Bradley thought he had a major headache on his hands.

A propane-air mixing station uses vaporizers and propane-air mixers to combine propane with ambient air, creating a mixture that can be used as a direct replacement for natural gas.

The Mississippi Department of Corrections (MDOC) facility was built in 1997 in Woodville, 30 miles south of Naches, to house 1,000 offenders. A prison of that size has a major gas load, with hundreds of gas systems, including boilers, water heaters, roof top unit heaters, commercial clothes dryers, and a commercial kitchen with dozens of appliances.

Wilkinson County Correctional Center uses hundreds of gas systems, including boilers, water heaters, roof top unit heaters, commercial clothes dryers, and a commercial kitchen with dozens of appliances, so converting from natural gas to traditional propane would have been time-consuming and costly.

Although the prison could run the same type of equipment by switching to propane, Bradley was concerned about the hassle and cost of converting so many appliances. “That would have been a very costly item to do that, because of the number of individual pieces of equipment that we have,” Bradley says. “We could make it work, but it would be a major inconvenience in the business that we manage every day.”

Wilkinson’s switch from natural gas to propane-air mix required no system downtime, helping maintain the integrity and security of the facility.

So when Bradley approached Pinnacle Propane about the conversion, he was relieved when the company proposed an alternative that wouldn’t require any conversions: a propane-air mix that is interchangeable with natural gas.

What Is Propane-Air Mix?

Also known as synthetic natural gas or SNG, propane-air mix is a replacement for natural gas where natural gas lines aren’t available or when a facility needs an onsite backup gas supply. It’s created by mixing propane and ambient air using vaporizers and propane-air mixers. Once it’s mixed, it can be used as a direct replacement for natural gas.

For the Wilkinson County Correctional Facility, using propane-air meant not having to modify any appliances or take segments of the facility offline, says Harris Baker, vice president of business development for Houston-based Pinnacle Propane.

“We built a tank site with a 30,000-gallon tank, and we built a redundant system, so it’s two parallel systems with a backup generator on them,” Baker says. “We just tapped into the existing natural gas infrastructure and just simply replaced it and switched to propane.” The team performed a full safety and leak check over a weekend and made minor adjustments to the gas mix. “Stoves, ranges, boilers, hot water — anything with a thermal demand was met perfectly and seamlessly with propane-air mix,” Baker says.

A Standby Solution

Wilkinson required a permanent replacement for its natural gas supply, but propane-air mix is also commonly used as a backup for facilities that might temporarily lose their gas supply or have it curtailed, says Angrest Harris, engineering manager at Ransome Manufacturing, a provider of vaporizers and mixers.

For instance, hospitals may be required to have a backup gas supply or choose to install one to make their facilities more resilient. Ransome recently provided a system for a Kaiser Permanente hospital in Harbor City, California, that was mandated to have a backup supply for the natural gas used to fuel the hospital’s boilers, cooking, and other gas equipment.

Industrial facilities are another common application because of their critical need for an uninterrupted gas supply. For a glass plant project in Kingsburg, California, losing the gas supply for the furnaces could ruin an entire line, causing massive financial losses. Ransome provided a propane-air mix system that seamlessly supplements the natural gas in the event of a loss or curtailment. “There’s companies like that where they just can’t afford to shut down their operations,” Harris says.

The need for a backup solution is most common in areas where the natural gas distribution line is undersized or under strain, Baker says. On high-demand days, the utility might interrupt and redirect the natural gas supply for large industrial users, perhaps even providing rate incentives to users that agree to participate and put a backup plan in place. Natural gas utilities may even employ propane-air mix themselves to supplement the natural gas supply.

An operation might also choose propane-air mix if they expect to have access to natural gas in the future. An almond orchard in Kerman, California, anticipated getting natural gas, but they weren’t sure when the lines would reach them. So Ransome installed a propane-air mixer to fuel the orchard’s dryers rather than simply using propane. “They’ve got these dryers, which is a pretty good expense for them,” Harris says. “When the time comes to switch over to natural gas, you don’t have to do all the regulator changes, you don’t have to do all the orifice changes on these burners.”

Where to Begin?

Facilities considering using a propane-air mix should begin by determining their potential connected gas load, Harris suggests. Ransome’s smallest mixer is about 15 million British thermal units (which would use about 180 gallons of propane per hour), so a small operation with a boiler or dryer could potentially use it. But the most economical applications are larger users.

The facility would also need space for a large propane tank, with setbacks from property lines and important buildings. A 30,000-gallon tank is the most common size, Harris says. The propane-air mixer setup requires electrical service, and a pump is generally needed if the site ever experiences weather below 40 degrees Fahrenheit. “It’s a moderate-sized project no matter what size of equipment you have,” Harris says. “It’s not necessarily an inexpensive project. It’s a capital expense.”

For facilities with critical needs like Wilkinson, which is privately operated for the MDOC by Management & Training Corporation, it’s a worthwhile expense to avoid the time and cost needed to convert and install new equipment.

“We’re all taxpayers,” Bradley says. “If we can do this in a method that’s efficient, cost-effective, and that will be a long-term solution, we’re not paying for the same equipment twice. It helped us facilitate what we needed to do to maintain the integrity of the facility, as well as the security that comes any time you are managing a prison operation.”

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Jeffrey Lee