New Technology Reduces Natural Gas Consumption

Installing draft regulator in exhaust stack improves boiler operations, thermal efficiency.
By Ed Sanchez | July 14, 2014

Making ethanol today is not unlike what the Hatfields did in Appalachia a century ago: set up a still, add the magic ingredients and make product. If you sat down and chatted with ethanol producers today, the process obviously is more sophisticated now. Among the many efficiency gains being sought today, they might talk about holding the line or possibly reducing the costs the company pays for natural gas per unit of product, or discuss ongoing efforts to reduce emissions.

The U.S. industrial sector accounts for approximately one-third of all energy used in the country, consuming 32 quadrillion Btu annually while emitting 1,680 million metric tons of carbon dioxide in the process, according to a May 2005 study of U.S. industrial commercial boilers by the Energy and Environmental Analysis Inc. About 40 percent of this energy consumed in the industrial sector is used to fire boilers to generate steam and hot water. Out of that, it is estimated that 20 to 50 percent of the energy used to fire boilers is lost as waste heat. On the high side, that equates to 6.4 quadrillion Btu lost up the stack. 

Since ethanol plant boilers are a subset, what solutions are available for operators to reduce wasted heat? Charles Stremick, chief operating officer of Plymouth Energy LLC, Merrill, Iowa, began reviewing the various technological approaches to improve fuel consumption and utilization for industrial boilers with varying cost benefit profiles. Efforts toward greater efficiency historically have been to install systems that will either focus on combustion processes or capture exhaust heat for use in preheating boiler feed water or combustion air, thereby reducing input Btu requirements for process heat loads. These technologies include, but are not limited to, oxygen trim systems, burner control packages, linkageless controls, economizers, flue gas recirculators, modulating dampers and variable frequency drive blower motors.

In larger power boilers, there exist modulating flue dampener systems designed to limit high-negative or excess draft. Excessive draft will pull heat out of the boiler sooner than necessary and before complete heat transfer can occur. Excessive draft conditions will cause an energy-efficient boiler to operate inefficiently (i.e., combustion and thermal). Optimized modulating draft control systems require a complicated interconnected system of hardware and sensors that cause the flue damper to open or close in response to boiler modulation as well as what is going on in the boiler exhaust stack. History has shown these complex systems are expensive and require a diligent maintenance effort to keep them calibrated.

During his research, Stremick came across a new proprietary technology created by Energy Conservation Management Inc. ECM’s draft regulator is an engineered solution that reduces flue stack velocities, allowing for improved heat transfer dwell time and reduced fuel consumption, while maintaining current process heat levels.

After careful review of the various technologies and the associated paybacks, Plymouth Energy chose the ECM solution. Working with its local partner, Efficium LLC, Sioux City, Iowa, ECM installed its  draft regulator (EDR) technology in both boilers at the Plymouth Energy facility in March.

Installed in the exhaust stack above the roof line, the design of the EDR provides a means to “tune” the boiler for optimal combustion and thermal efficiency, while meeting system load demands and reducing fuel rate consumption at low, medium and high fire rates. Highly developed installation protocols are used to reduce natural gas inputs, excess combustion air, exhaust gas stack temperatures, exhaust velocity and nitrogen oxide (NOx) emissions. These reductions are coupled with improvements in combustion efficiency and fuel-to-steam efficiency, without a reduction in the boiler’s ability to produce steam. A properly installed and tuned EDR leads to a reduction in boiler fuel consumption as illustrated in the accompanying table showing pre- and post-installation stack readings at Plymouth Energy.

Proper installation and tuning of the EDR also increases heat transfer dwell time, resulting in improved heat production level (psi/min)  with an increase of 3.9 percent within the boiler system as presented in the accompanying table on Steam Production Rate Testing. The importance of heat transfer dwell time, along with creating an environment for complete combustion, results in a more rapid process heat production capacity with less fuel input.

In addition, the reduction of consumed fuel per unit of product reduces the negative emissions into the atmosphere. Once the ECM/Efficium team performs the diagnostics of a specific boiler, we quickly determine if this device is beneficial for the client. The unit is installed according to specific procedures, protocols and measurement parameters that ultimately lead to a “hands off” device for the next 25 years.

When asked how he reached a decision to install the ECM solution over the other technologies utilizing stack gas restrictions, Stremick said, “We looked at other systems, but the cost was much higher and the install required downtime for the plant.” The time targeted for the proposed ECM install was going to coincide with Plymouth Energy’s high margin months, which meant it was imperative that an installation could not affect production. 

Plymouth Energy had previously added several other features to its 2,200 HP Superior, two-pass, dry-back, fire tube power boiler, including a Webster burner, AutoFlame burner control system, oxygen trim, linkageless parallel positioning, and flue gas recirculation system with a Cain economizer and a fixed-drive combustion air blower.

When the results of the installation were complete, ECM presented its findings to the plant management team.  “The results did surprise me a bit,” Stremick said. “They guaranteed 4 percent (in fuel savings) and beat their guarantee by a good margin (almost 2 percent). We are very detailed about tuning our boilers with seasonal changes to make sure they are running as efficiently as possible.” That 6 percent savings goes right to the win column for the company. The white paper on the installation is available at from ECM.

Stremick also pointed out his company was pleasantly surprised by two additional benefits, the first being the elimination of their “boiler rumble,” which is a thermal acoustic harmonic event that often occurs in large power boilers, and second, the notable reduction in the production of NOx emissions. “The NOx was reduced by approximately 38 percent on one boiler and nearly that much on the other boiler as well. This makes a green company even greener and more competitive in certain states and countries,” Stremick said.

Author: Ed Sanchez
Director of Engineering,
Energy Conservation Management
480-443-2397
esanchez@ecmgmt.net

Contributing Author: Jim Hatfield, freelance writer, Scottsdale, Arizona

 

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