Low Nox Dryers - Know Your Limits

Operators in California and other states face increasingly tight restrictions on dryer-air emissions

California is again taking the lead nationally in enacting some of the toughest emissions-control standards and setting the stage for other states to follow in its footsteps.

Vehicle emissions are at the forefront of the latest push, as are other gas- and diesel-fueled emission sources. However, another target has been industrial emissions from sources such as generators, boilers, and in the laundry industry in particular, industrial dryers. For years, California has established these tough standards. Although this article is based on California standards, they soon may apply in your state or local code jurisdiction as well.

So as a laundry operator in California, specifically Southern California, you’ve decided it’s time to replace your less-than optimally efficient industrial dryers. You plan to invest significant capital in this replacement and want to be sure that your new dryers have the latest features, as well as solid efficiency and performance capabilities. They also must meet your laundry’s capacity requirements. In short, you want to ensure that you’re getting the best possible return on investment (ROI). Well, there is one more criterion that you need to pay attention to…air emission requirements. You’ll need to ask your manufacturer if the new dryers will meet the stringent requirements for air emissions governed by the South Coast Air Quality Management District (SCAQMD). Let’s take a look at how these rules might impact your decision, and give you the facts you need to discuss this topic with manufacturers as you evaluate your solution options.


The Federal Clean Air Act of 1963, followed by major amendments in 1970, 1977 and 1990, established a framework for the ever-tightening regulation of nitrogen oxides (NOx) and carbon monoxide (CO) emissions. The act also allows states to establish even tighter requirements for air emissions standards, which the state of California has done. Specifi cally, SCAQMD established rules for all types of emissions sources. Every source, from vehicles, to power plants, to industrial equipment, is covered under these regulations. This article will focus on industrial dryers in particular. If you’re interested in other rules governing other types of equipment that you may be using, consult the SCAQMD website at www.aqmd.gov.

For industrial dryers, SCAQMD Air Quality Rules for miscellaneous NOx Sources (Rule 1147) covers the use and emissions from industrial dryers. In general, this requirement mandates that the dryer can emit no more than 30 parts per million (ppm) NOx and no more than 400 ppm of CO. Although specifi c to SCAQMD, many other districts in California and elsewhere across the United States have similar (if not identical) limits and rules covering emissions. For the purposes of this article, we will only focus on Rule 1147 and how it impacts your buying decision regarding new dryers.

So, to evaluate how this rule, and these regulations that apply to your individual situation, you must define how the new dryer will be used. Specifically, what type of goods will be run in the dryer? Will a product that may contain Volatile Organic Compounds (VOCs) be dried? These would include products like shop towels, bar towels, and any other products that could have solvents, grease, etc. The answer to these questions is extremely important because it may allow you and the dryer manufacturer to take advantage of an exemption to Rule 1147.

Rule 1147 states that if your equipment has a heat input rating of less than 2 million BTU per hour, it only burns natural gas, and it has no other emissions other than the products of combustion, it would be exempt from air permitting. How does this impact your potential decision on a purchase? Stay tuned.

If you’ve evaluated your products and determined that there may be some that contain VOCs, then the exemption noted above won’t apply to you, and the dryers you select must be capable of meeting the limits for NOx and CO. Now you are ready to ask some questions of your prospective vendor for the new dryers.

The first question is based on the assumption that you won’t be processing any product that contains VOCs. That question is: What is the maximum output of your dryer?” If the answer to this question is an output greater than 2 million BTU per hour, then you’d have to permit that dryer unless the answer to the next question is “yes.” That question is: “Can you ‘detune,’ or reduce the power of the gas train of your dryer to a maximum output less than 2 million BTU per hour and denote it on the dryer’s serial nameplate?’ Assuming the manufacturer tells you they can, this move, in combination with the fact that you won’t be processing any goods containing VOCs, will exempt you from filing air permits for this equipment.

However, there is one last question for the vendor in this case; “How will detuning your gas train impact your stated efficiency numbers and turn times?” Detuning a gas train can and will impact some manufacturers’ efficiency and turn times. Others rate their equipment for the lower detuned numbers up front. Still others have dryers that actually suffer no measureable losses when the gas train is detuned. The key is to understand how the lower BTU output you are forced to run with will impact natural gas usage and productivity (or turn times). These benchmarks typically are stated by a manufacturer, based on the maximum BTU output capability of the industrial dryer.


Now we’ll move on to the second scenario. If you are going to be drying product such as shop towels or bar towels that contain VOCs, or you have already decided on a specific manufacturer that cannot detune their gas train below 2 million BTU per hour, your new dryers must meet the requirements as stated previously— 30 ppm NOx & 400 ppm CO. Now things get a lot more complicated as far as compliance with SCAQMD (or other local districts in your state) permitting rules. The intent of this article is not to dig into these rules and regulations, but rather to help you ensure that the new dryers you are going to purchase will meet those requirements.

When you begin the search for a true low NOx-capable industrial dryer, you need to ensure that the dryers you are about to purchase actually are capable of meeting the stated NOx and CO emissions standards for your area. Manufacturers may claim their dryers are “low NOx,” but in reality, they are simply using a burner that’s rated as a low NOx burner. However, if the burner doesn’t have the controls to go along with it to allow the dryer to meet these low-emission requirements, it will not comply with low NOx standards, and will not be supported by the burner OEM. One easy way to determine whether the dryer in question actually meets the standards or is just being “advertised” as meeting them is to ask your prospective vendor for a letter certifying that the dryer will meet the stated standard for NOx and CO emissions. In the case of SCAQMD, that is 30 ppm NOx and 400 ppm CO. If the manufacturer won’t or can’t give you that certification, you should walk away. Why? Because that means that they can’t assure you that the system will comply with air-emission requirements. Purchasing such a dryer could mean investing a large amount of capital only to find out that you can’t run the equipment once it’s installed. Even if your manufacturer provides a certification, be aware that in most cases you’ll still have to hire a third-party testing agency to test the dryers and certify them for your air permit. If this testing shows the dryer doesn’t meet the standards, and you have a letter from the manufacturer certifying that it will, you now have leverage to hold that vendor accountable for making whatever adjustments or changes are needed to comply with the standards. Without that certifi cation, you could be left with dryers that won’t be doing any actual drying, or at best, they’ll need to be detuned and you won’t be able to dry products containing VOCs as you’d intended.

In order to keep your dryer running at peak effi ciency and maintaining the stated emissions standards, you must perform routine maintenance on the dryer, per the manufacturers’ recommendations. Manufacturers that certify emissions standards typically only certify these emissions under their warranty period and only if the dryer was maintained in accordance with recommendations from the manufacturers’ manual(s). One of the most critical items is keeping the combustion air balance by cleaning the combustion fi lter every day. Another may be checking and maintaining the correct incoming gas pressure. This is a step that the owner should perform on the schedule outlined in the dryer’s manual. If sound preventative maintenance is performed on a routine basis, the dryer will continue to produce goods in an effi cient and productive manner, and it will also continue to meet the emissions standards stated from the manufacturer. However, if preventative maintenance isn’t performed regularly, emissions may slip above limits, and the dryer may begin to lose the effi ciency and productivity (energy use and turn times) it had when it was installed. In this case, the dryer may exceed the limits on its emissions certifi cation, thus leading to costly repairs or readjustments of the gas train and/or its components.


In summary, the regulations governing air emissions are changing rapidly, and keeping up with these changes isn’t easy. As an operator—and a producer of NOx and CO—it’s your responsibility to keep abreast of these regulations as they pertain to your equipment emissions. To serve your best interests, you must understand how these rules will impact equipment in which you’re considering investing thousands of dollars. Make sure that you do your homework. Ask the right questions, and obtain certifi cations from your vendor if necessary before pulling the trigger on that large investment.


ABOVE: (l/r) Here is a view of a low NOx burner in a dryer; a graphic image of a low NOx burner; on the opening page, there is a group of three low NOx dryers in operation in a plant.

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