Keywords 11Downstream processing, distillation, dividing-wall column, optimal design, process control 12
13
Highlights
14• Energy efficient downstream processing in the acetone-butanol-ethanol (ABE) process 15• Cost effective distillation process for butanol separation and purification 16• Optimal process design including heat-integration, still robust and controllable 17 18
Abstract 19Butanol is considered a superior biofuel, as it is more energy dense and less hygroscopic than 20 the more popular ethanol, resulting in higher possible blending ratios with gasoline. However, 21 the production cost of the acetone-butanol-ethanol (ABE) fermentation process is still high, 22 mainly due to the low butanol titer, yield and productivity in bioprocesses. The conventional 23 recovery by distillation is an energy-intensive process that has largely restricted the economic 24 production of biobutanol. Other methods based on gas stripping, liquid-liquid extraction, 25 adsorption, and membranes are also energy intensive due to the bulk removal of water. 26This work proposes a new process for the butanol recovery by enhanced distillation (e.g. 27 dividing-wall column technology) using only few operating units in an optimized sequence to 28 reduce overall costs. A plant capacity of 40 ktpy butanol is considered and purities of 99.4 29 %wt butanol, 99.4 %wt acetone and 91.4 %wt ethanol. The complete downstream processing 30 was rigorously simulated and optimized using Aspen Plus. The enhanced process is effective 31 in terms of eco-efficiency (1.24 kWh/kg butanol, significant lower costs and emissions) and 32 can be readily employed at large scale to improve the economics of biobutanol production. 33
Keywords 12Bioethanol dehydration; process dynamics; process control; integrated design; heat pumps 13 14
Highlights
15• Highly integrated design leading to challenges in process dynamics and control 16• Efficient control structure ensuring stable operation of VRC assisted E-DWC 17• Disturbances in feed flowrate and composition can be effectively rejected 18 19
Abstract 20Recently, a novel heat-pump-assisted extractive distillation process taking place in a dividing-21 wall column was proposed for bioethanol dehydration. This integrated design combines three 22 distillation columns into a single unit that allows over 40% energy savings and low specific 23 energy requirements of 1.24 kWh/kg ethanol. However, these economic benefits are possible 24 only if this highly integrated system is also controllable to ensure operational availability. 25 This paper is the first to address the challenges related to process dynamics and control of this 26 highly integrated system. After showing the control difficulties associated with the original 27 design owing to thermal unbalance, an efficient control structure is proposed which introduces 28 a by-pass and an additional external duty stream to the side reboiler. The range of the external 29 duty is rather small, about 5% of the combined duty of the reboilers, but sufficient to stabilize 30 the system by controlling the temperature on the pre-concentration side of the column. Two 31 quality control loops ensures product purity when the system is affected by feed flowrate and 32 composition disturbances. 33
34Dynamics and control of a heat pump assisted E-DWC for bioethanol dehydration Patraşcu, Bîldea, Kiss 2
The biobutanol stream obtained after the fermentation step in the acetone−butanol−ethanol process has a low concentration (less than 3 wt % butanol) that leads to high energy usage for conventional downstream separation. To overcome the high downstream processing costs, this study proposes a novel intensified separation process based on a heat pump (vapor recompression)-assisted azeotropic dividing-wall column (A-DWC). Pinch analysis and rigorous process simulations have been used for the process synthesis, design, and optimization of this novel sustainable process. Remarkably, the energy requirement for butanol separation using heat integration and vapor recompression assisted A-DWC is reduced by 58% from 6.3 to 2.7 MJ/kg butanol.
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