Let’s Talk About Dew Point –
Levi and Perry from P.C. McKenzie Company
explain Dew Point from the Gas Compression
and Boiler side of our Business –
Dew Point from the Gas Compression Side – Levi Explains
Dew point, it’s important. In my experience over the years in gas compression, I have learned just how important monitoring and controlling the dew point of compressor station gas is. What I didn’t know is that dew point is also very important in the boiler world. After looking at an article about a condensing boiler and seeing that all too familiar “dew point” term, I realized that dew point plays an important role in boiler world too. Interesting. Since I have experience with the gas compressor side of this subject, let’s start there.
Before we dive into how dew point effects these systems let’s define what it actually is. Webster defines it as: “the temperature at which a vapor (such as water) begins or would begin to condense.” In every day terms, this means it is the temperature that vapor starts to drop out as a liquid, dew on the grass in the morning being the easiest example. This is extremely important in gas compression because we want to deliver compressed gas, and only compressed gas, to your CNG vehicles.
PC McKenzie has always told our customers that we offer excellent gas compressors, but these compressors make terrible pumps! I cannot overstate the need to eliminate all liquids, or hydrates (a topic for another time) from the gas that might form as a result of compression.
The two main processes we use to set ourselves up to ensure our gas is as dry as we can make, and in turn have a very low dew point, are filtration and dehydration. Filtration is the more straight forward of the two processes. We use filters to remove liquid out of the gas stream. Dehydrating is the more nuanced process and it is generally done with a desiccant drying tower. In this process the gas comes in from the utility and is immediately run through a gas dryer filled with desiccant beads that strip moisture out of the gas through adsorption. These beads (think magnets, not sponges) hold on to moisture until they are heated to a high enough temperature to release them.
Lowering the dewpoint of gas before it is compressed is important because we do not want our compressors encounter any added wear and tear, like compressing moisture out of a gas, and also the more you compress a gas the higher the dew point gets!
Dew points are important. In gas compression, the more moisture we can strip out of the gas the lower we can make the dew point. The lower the point the less wear and tear on our systems. I hope this was helpful and not too confusing. –
Please visit our Natural Gas Compressor Page to see what we offer in natural gas for refueling.
Below I’m going to leave it up to Perry, our boiler guru, to talk about why dew points are so important on the boiler side of the house.
Dew Point from the Boiler Side – Perry Explains
Condensing boilers get their name for the ability to collect the energy form condensate. They reach their highest efficiencies when operating at part load and when they are condensing.
So, how do we get condensing to take place? It’s all about the dew point of the products of combustion and the temperature of the heating hot water returning to the boiler. If we can get the return water temperature below the dew point of the flue gas, we can get the vapor in the flue gas to condense. This condensation contributes 1,000 BTU per pound of condensate transferred into the water without using any additional fuel.
Boilers need oxygen to fire. Typically, an excess of oxygen is pushed into the boiler in order to produce a stable flame. The trouble is that the higher the excess oxygen level, the less carbon dioxide there is in the exhaust. And, the lower the carbon dioxide level, the lower the dew point temperature. Remember as Levi mentioned the dew point temperature is “the temperature that vapor starts to drop out as a liquid”. So, If the return temps never get low enough and close enough to the dew point the boiler will not condense. Depending on the boiler reset schedule, you may own a boiler that never condenses. Which if you have paid for a condensing boiler is money down the drain
How can you tell if your boiler is condensing? Few ways, first check your return temps if its not lower than 140°F condensing is highly unlikely. Secondly is check the drain on the exhaust/bottom of the boiler. (Be careful not the water side, we are talking about the condensate drain on the fireside of the boiler) if there is condensate (looks like water) coming out congratulations you are squeezing the most out of your exhaust gasses.
Condensing boilers can be tricky with a lot of buzz words flying around. We represent Patterson Kelly boilers made here in my home state of Pennsylvania. They have been in the condensing boiler game for a long time and have a lot of experience. If you have any questions feel free to reach out to us or Patterson Kelley and together we can get you condensate you deserve.
To contact us with questions or find helpful CNG/NGV/Hot water and Steam boiler service tips, please check out our website www.mckenziecorp.com under the resources tab.