Cellulosics Conversion Gets a Boost

Control system enhances operation of demonstration plant.

By Rich Chmielewski, Marketing Manager, Siemens Industry

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3. Product concentration. Water concentration is adjusted and formic acid and furfural, if present, are recovered.
4. Recycle acid separation. Product is removed from the acid, which then is recycled.
5. Product recovery. Product either is converted to derivative products or further purified, if necessary.

Process Advantages
The technology boasts several important advantages over other levulinic acid and cellulose conversion ones:

Compactness. The reaction is fast, so residence time in the reactor system is short and a small reactor volume can provide a high throughput. The process is sufficiently compact that an ocean-going "Panamax" barge can accommodate a self-contained 1,000-ton/day unit, according to a feasibility study.

Low cost. The only reaction catalyst is low-cost dilute mineral acid that's recycled within the process, eliminating the need for disposal of waste salts.

Feedstock flexibility. The process can handle a wide range of low-grade variable-composition cellulosic feedstocks or proposed dedicated energy crops such as willow, poplar, miscanthus grasses or switchgrass.

Robustness. The conversion chemistry only depends on dilute-mineral-acid-catalyzed hydrolysis of carbohydrate polymers and is unaffected by contaminants typically found in waste feedstocks.

Ease of operation. Hydrolysis occurs continuously. This affords the potential for significant process energy integration and reduces equipment size and labor requirements as well as maintenance and energy costs compared with comparable batch operations.

Byproduct flexibility. Byproduct credits don't significantly affect process economics. It's easy to convert the furfural byproduct from hemi-cellulose to levulinic acid (via hydrogenation to furfural alcohol), thereby markedly increasing yield of the main product. Formic acid can be sold or converted to derivatives.

Energy self-sufficiency. The char byproduct contains sufficient energy to satisfy all the steam and electric power needs of the process. At larger scale (above 300 t/d), the process produces significant excess power that can be exported to the grid.

The Importance of the Control System
At the heart of the demonstration plant is a Simatic PCS 7 process control system from Siemens Energy & Automation. The control system, installed and programmed by Siemens solution partner Optimation/Dumont Associates, includes redundant dual-screen operator stations communicating over industrial ethernet to the control processor (Figure 1). The PCS 7 system uses a Profibus fieldbus network to communicate with input/output (I/O) modules and 20 Siemens Micromaster variable frequency drives (1 hp to 5 hp) controlling agitators and pumps.

The focus of the project was to enhance productivity of the plant's startup and shutdown processes by capitalizing on past successes, says Joe Doherty, project manager at Optimation/Dumont Associates, which has worked with Biofine Renewables on previous related projects over the years and has a long-established relationship with Siemens.

"We won the project when Biofine Renewables moved its plant from Glen Falls, N.Y., to Gorham," Doherty notes. "Fitzpatrick operated another plant that used the Siemens PCS 7 control system. It worked out so well for him that he wanted to use the same control system for this newly located plant."

Operators monitor the demonstration plant from a central control room equipped with an engineering station and two redundant operator stations.

Doherty says 50 different interlocks are programmed into the system. Operators can safely and efficiently override interlocks when required, allowing the process to continue under close supervision.

"If something does happen, the PCS 7 system can quickly identify the cause," he notes. "In a continuous process, something like a low level alarm in one tank can cause the entire downstream process to shut down, so it is critical to quickly identify the issue. The PCS 7 system consistently maintains the steady state and makes adjustments automatically."

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