Abstract
There are various outlets for disposal and utilization of the crude glycerol generated in biodiesel plants in Thailand. For large scale biodiesel manufacturers, crude glycerol can be refined into a pure form and then be used in food, pharmaceutical, or cosmetics industries. For small scale manufacturers, however, purification is too expensive to be performed in their manufacturing sites. Their crude glycerol is usually sold to large refineries for upgrading. In recent years, however, with the rapid expansion of biodiesel industry, the market is being flooded with excessive crude glycerol. As a result, biodiesel manufacturers only receive 0.07 - 0.1 US$/kg for this glycerol. Therefore, manufacturers must seek new, value-added uses for this glycerol.
In order to convert crude glycerol into valued-added products through thermo-chemical methods with an alternative for utilizing this waste stream. This paper focuses on the conceptual design for the production of a promising biofuel source out of waste glycerol to be integrated within a small stand-alone biodiesel plant in the south of Thailand. The biodiesel production plant used in the process model, is supposed to give about 46,000 tons of crude palm oil per year. To produce this amount 14,735 kg/d raw glycerol material is needed. The simulation program proposes a detailed superstructure embedding the alternative technologies involved. The commercial simulators ASPEN Plus is used to construct the process modelling, simulations and economic potential are performed to investigate different conditions for an integrated plant. Briefly, glycerol as a waste product from the trans-esterification of small plant oils and animal fats is first reformed using steam reforming. By concept, the syngas obtained is cleaned up and its composition is adjusted in terms of the ratio H2/CO and then fed to the Fischer-Tropsch (FT) reactor. The novelty of this process lies in the use of a Ruthenium-based catalyst for the conversion of syngas to synthetic fuels. RYield model based on experimental data is used for formulating the product distribution of hydrocarbons (C5-C20) as stated by Anderson-Schulz-Flory (ASF). The synthetic fuel production is to be approximately 2,692 L/d in which overall conversion per pass equals to 35%. The production of FTs liquid is separated while the off-gas as by-product is using for cogeneration with gas engine system to produce the electricity.
For providing good asset out of the glycerol based on current market prices, the analysis reveals that the production is economically feasible, with a production cost for the hydrogen of $4.71/kg, but still struggling to survive in business for reaching adequate profit. Meanwhile, the results from the FT process simulations, along with an economic evaluation, appear to be a very promising technology for synthetic fuel production, but the cost structure for benefit makeup is still under study. Noticeably, the integrated process simulation is as effective as possible and both the secondary steam from pre-treatment and steam drying would be used in the reforming and FTs plant, to knock down the production cost.
