By Dennis Zeedyk, Lee Enterprises Consulting
Special to The Digest
Glycerin Traders LLC’s flagship operation, based in Defiance, OH, takes in waste raw glycerin from biodiesel companies and acidulates it to remove the fats, methanol and some water that is then further distilled to nearly 100% purity.
This year the Defiance plant spent an average of about $15,000/month on natural gas to power the 5.5 million BTU boiler tank and approximately $3,300/month to the city for water usage. Its boiler constantly runs on high-fire, fueling the plant’s three glycerin processing lines and methanol distillation column. Because the business is always looking for ways to cut costs and conserve energy, it quickly learned from key advisors and experience, the importance of good boiler management. The secret to longevity is to focus on maximizing the water’s usage and heat consistency. This will save money and reduce wear and tear on the machine.
A boiler creates steam by applying heat energy to water using a variety of different fuels such as natural gas, propane, diesel or biodiesel. The most common steam boilers used are fire-tube boilers (pictured below). These operate by having the fire flow within the tubes to heat the water surrounding them. In some cases, the hot gases pass back and forth up to three times, increasing heat transfer with each pass, before the exhaust passes through the chimney and the steam is pushed down the line. These boilers are very rugged and less prone to failure making them easier to operate than water-tube boilers. With water-tube boilers, water flows on the inside of the tubes and the fire surrounds them. These typically operate at 1-290 psi.
Figure 1. On the left is a graphic describing the fire-tube boilers. These push the heat from the inside of the tubes to create steam from the water tank. The photo on the right is an example of a water-tube boiler, which heats the water-filled tubes from the outside.
When water is converted to steam it expands in volume 1,600 times – allowing it to travel down steam pipes at over 80 feet per second. If the steam is pressurized (for example to 125 psi), it will occupy less space and can be produced by a smaller boiler with smaller bore pipes. The steam pressure is later relieved at the point of use which will either be in the steam coils or heat exchanger.
Steam is great for transferring heat and energy around a site from the boiler to where it is needed. The pipes that contain this flow of energy are made up of; booster pumps for the steam, heat exchangers for heat “extraction” which increases the temperature of the product (in Glycerin Trader’s case it is glycerin or methanol), and the steam itself is ultimately turned back into hot water after the heat exchanger. This recycled hot water that has been condensed from cooling steam is known as condensate. Steam traps use steam power to push the condensate back into the relatively hot boiler feed tank. The collected condensation feeds the boiler to start the process all over again.
The return of the condensate to the boiler is exactly where the cost savings are manifested. By capturing and using this recycled hot water, the boiler will use significantly less incoming city water. Equally important, it reduces the fuel bill (natural gas) as the incoming water is cold and requires more natural gas in order to heat it back to steam. The returning condensate is already 190 F, reducing the amount of fuel required to get the water turned back to steam. Returning condensate also helps the boiler tubes last longer due to reduced temperature shock that would occur with incoming city water. To summarize, recycling condensate as opposed to incoming city water reduces water usage, natural gas usage and increases boiler longevity.
To adequately capture condensate, the condensate lines may need to be re-piped, adjusted, or remodeled with a new steam pump and different style steam traps. This may seem like a lot of repairs and investments, but keep in mind that the boiler is probably the largest user of fuel and water in a biodiesel plant. Glycerin Trader’s numbers have shown that these changes make the extra effort worth it in the end.
During a one-week period in May, the Defiance plant was forced to run its condensate into a special tank for disposal as opposed to the normal operation of returning it to the boiler feed tank. This was done to flush some vegetable oils that ended up in the boiler as the result of a leaking heat exchanger. While this was done for only one week, the cost for water went from $3,300 to $4,300 – a 30% increase in just 7-days. Had this continued for a month, costs would extrapolate to 2.2 times as high in water usage alone. This does not take into consideration the increase in natural gas usage for boiling the incoming 57o F city water as opposed to starting with the already 190o F returning condensate (which couldn’t be tied to an exact dollar amount during its short window of time).
Another way to practice good boiler management is to use quality soft water. It is very important to treat the boiler feed water in order to prevent scale formation and corrosion. Scale and corrosion will decrease energy transfer efficiency, increase energy costs and lead to poor quality steam, shorter plant life, and an unreliable operation. While variations in quality standards may exist in different states and countries – stringent legal, testing, training and certification should be applied to minimize or prevent such occurrences.
The Defiance facility uses a dual softener system with two chemical pumps; one to remove oxygen from the water and the second to treat the boiler water. This ensures that the boiler is always being fed soft water. A column blow-down is performed at least once per day to ensure the sulfites are removed and the safety switches always work. A third chemical treatment of the condensate prevents pitting of the pipes on the way back to the feed tank. Lastly, bottom blow-downs are performed twice a day to remove the total dissolved solids from the bottom of the boiler. This is usually done at the end of each shift. When all of these things are taken into consideration, it prevents catastrophic failure of the boiler.
The Defiance boiler uses approximately 8,000 gallons per day (GPD) – primarily lost through evaporation, steam leaks, blow-downs, and condensate purging. This water is NOT returned to the city sewer. The city of Defiance doesn’t monitor or measure the amount of sewage returning to the water treatment plant and instead uses a formula based on city water usage to determine the amount to charge for sewage. Because this 8,000 GPD is not returned to the city, GT requested a separate meter for the boiler. This same amount is subtracted from Glycerin Trader’s sewage bill, thus lowering the total water bill.
In conclusion, cost savings from boiler operations are obtained by the following practices:
- Re-using condensate lowers the cost of water intake from the city.
- Having a separate meter to determine actual boiler water usage subtracts from the sewage bill.
- Natural gas bills are reduced when less energy is used to create steam.
- The boiler will last longer due to the re-use of condensate, timely blow-downs and the use of appropriate chemicals used for water treatment.
Keeping the boiler running well over a long period of time while simultaneously reducing costs is one more step to staying afloat in the business economy we live in today.
About the Author: Dennis Zeedyjk is an independent consultant and member of Lee Enterprises Consulting Group. The opinions expressed herein are those of the author and do not necessarily reflect the opinions of Lee Enterprises Consulting.