Many industrial manufacturers rely on boilers to provide hot water and steam to their plants. But boilers can be expensive to run, especially as fuel prices fluctuate.
Olin Chlor Chemicals, a division of Olin Corp., Clayton, Mo., relied on a neighboring facility to supply steam to its manufacturing operations in Niagara Falls, N.Y. In 2001, Olin’s steam supplier announced that it would be closing its facility.
This posed a significant problem for Olin, a manufacturer of chlorine and caustic soda, hydrochloric acid, hydrogen and bleach products. The steam its neighbor once supplied was used in its manufacturing process and its building heat. In short order, Olin was faced with the task of installing a new boiler system of its own. Faced with an unexpected expense and rising fuel prices, Olin desired a creative solution that would generate lower fuel costs than what the company was paying with its previous steam supplier. At the same time, environmental responsibility was of concern to the company as well.
At the time, Olin was producing an excess of hydrogen byproduct gas. The company used part of that H2production in its process and also was selling some volume. Because H2gas is difficult to store, excess H2was vented.
One way to reduce the overall operating costs of a boiler system is to use alternative fuel sources. Some industrial boilers can burn both traditional fuels, such as gas and No. 2 oil, and alternative fuels, such as biodiesel and ultra-low sulfur diesel. With this capability, manufacturers can burn traditional fuel when the prices are lower and then switch to the alternative fuel during peak times, reducing boiler operating costs by as much as 75 percent.
The Olin team realized the company could substantially reduce its annual fuel costs by burning the excess hydrogen. The environmental side effect was welcome too as hydrogen combustion does not produce any CO2.
An Integrated SystemTo make the H2system a reality, Olin’s facility engineers contacted C-B Nebraska Boiler and C-B Natcom, the watertube boiler and burner divisions of Cleaver-Brooks, Milwaukee. Cleaver-Brooks installed two industrial watertube boilers with an output of 75,000 lb/hr each and operating pressures of 150 psig.
Conquering Challenges.Because H2is a processed gas, its availability is not constant. For that reason, the engineers at Olin wanted a system that could fire H2, natural gas and No. 2 oil to secure steam production. Another challenge C-B Natcom faced was that Olin’s H2supply pressure was relatively low. However, to maximize the fuel savings, Olin needed its burners to burn efficiently at both the boiler’s smallest possible pressure (flow) and its maximum capacity flow.
Available H2pressure was limited to 7 psig. To fire H2safely, it was essential to maintain a minimum velocity at the H2injectors. When turning down the capacity, a system typically uses a flow control valve to reduce available flow and pressure, resulting in a reduced firing rate. To overcome this limitation, C-B Natcom designed a burner that uses multiple H2injection zones. Much like car transmission that will shift gears to keep the engine RPM within the usable range, the burner injection zones open and close to kept the fuel pressure within the usable pressure limits. To meet the targeted 20:1 H2turndown (turndown is the ratio of the minimum firing rate to maximum firing rate), a system of six specifically sized injection zones was developed.
The low H2supply pressure, combined with high turndown ratio, created a need to specially design flow elements to minimize pressure drop. To ensure a representative flow signal throughout the turndown range, high differential pressure or pressure loss is typically required. In this situation, C-B Natcom worked with the instrumentation supplier to develop a split-range strategy for the flow elements to ensure safe, accurate flow signals with minimal pressure loss throughout the firing range.
Finally, the burner management system (BMS) and combustion control system (CCS) were developed to safely and efficiently manage five individual firing modes:
- Natural gas only.
- No. 2 oil only.
- H2 only.
- H2 with natural gas.
- H2 with No. 2 oil.<./ul>These options provide process control flexibility and the ability to adjust as needed to accommodate H2 supply availability and fluctuating fuel rates.
The system has an H2 main train that is 8" and a low-flow bypass for partial load H2 flow measurement of 3".
ResultsAs mentioned previously, an added benefit of burning hydrogen is that it is a clean fuel, meaning no CO2. However, H2is a rapidly burning fuel that inherently produces high levels of thermal NOX(in excess of 300 ppm). Olin’s targeted NOXlevel requirement when firing H2was 0.1 lb/MMBTU (110 ppm).
To accomplish this low NOXgoal, Cleaver-Brooks incorporated its Hyper-Shield technology into the burner. This technology injects steam around the periphery of H2injectors to shield the H2fuel from the oxygen being delivered by combustion air. This results in staged burning of of the hydrogen gas, reducing NOXformation. The resulting NOXemissions when firing H2fuel with sustaining natural gas were, on average, 72 ppm -- well below the targeted 110 ppm goal. Equally pleasing, when burning natural gas and sulfur No. 2 oil, Olin achieves low NOXlevels of 40 ppm and 110 ppm, respectively. With results such as these, Olin’s facility managers have been pleased with how much the new boiler system has helped lower the plant’s fuel costs.
Olin is saving approximately $2.5 million a year because of the technology allowing it to burn alternative fuel. This benefit allows the manufacturer to use the savings toward enhancing research and development to create new products and services and expand sales team -- desirable business activities in today’s competitive marketplace.
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