Biodiesel production from microalgae in Thailand

Abstract

This is a student assignment for the Norwegian oil and gas company StatoilHydro, The aim of this study is to investigate the potential of large scale production of biodiesel from microalgae. Since the technology is new and no large facilities exist to date, this report focuses on suitable technologies for future biodiesel production. There exist many different algae strains with high oil content e.g. Phaeodactylum tricornutum, Nannochloropsis salina and Botryococcus braunii. The alga Botryococcus braunii was first selected for large scale biodiesel production, but after encountering many problems when looking into the process, the string of Nannochloropsis salina was chosen instead. The high hydrocarbon content of B. braunii was one of the key factors when this alga initially was chosen, together with the algae’s ability to produce hydrocarbons during growth without the use of methods such as nitrogen starvation. Difficulties encountered when using this alga strain were separation problems since B. braunii has its hydrocarbons on the outside connecting the colonies, hence it is quite slimy. At the same time the colonies could be an advantage since the larger size means an easier separation. The fact that B. braunii is a fresh water algae is a big disadvantage in large scale production of biodiesel, if not having fresh water readily available, since this require a large desalination facility. Nannochloropsis salina on the other hand is a halotolerant string that prefers saline water similar to common seawater and has characteristics of producing high oil content within its cells. Nannochloropsis salina is therefore the alga strain used in this feasibility study for large scale biodiesel production. It is concluded that the most promising reactor type is the closed photobioreactor, since the other main alternative, the open pond, suffers from contamination risks, high evaporative losses of water and diffusion losses of CO2. Among the different types of closed photobioreactors; tubular, flat and polyethylene bags, the tubular seems to be the best choice since it has a higher photoefficiency than the flat reactor. The polyethylene bag reactor still needs developing and is not yet a viable alternative. After the algae have been harvested it is suggested that an increased dry weight is accomplished by a flocculation and sedimentation stage. The chosen method for the disruption of the cells is the utilization of a hydrodynamic cavitation process, followed by a stirring settling tank, where the oil floats and the cell debris sediment. Since hydrodynamic cavitation is a relatively unknown method, an alternative process using a wet bead mill for the cell breakage is presented as an alternative. However calculations are only performed on the former process alternative. In order to minimize losses in further refining and fulfill the EN 14214 standard for biodiesel production, the algal oil will in most cases need some kind of pretreatment. The most important purification steps will be degumming, which removes phosphorous content, as well as reaction of free fatty acids into methyl esters in order to avoid soap formation in the transesterification process. Suitable plant locations for StatoilHydro to put up a large scale biodiesel production facility are Qatar, South Africa and Australia. All cost estimates are made for a plant location in South Africa where the most suitable conditions can be found. The following factors showed to be most accountable in the cost estimates of this production facility: The productivity of algae Lifespan of the photobioreactor Interest rate on capital for investment Harvesting concentration Different scenarios were estimated and the production cost ranges from 0.38 €/L to 1.95 €/L between the best and worst case scenario with 0.87 €/L as the base case. An approximation that has been made is that nutrient/flocculant cost and algae meal revenue will balance each other. If the algae meal turns out to be worthless this will increase the algae oil price by 0.26 €/L and hence could be fatal to the biodiesel production from microalgae. The price of comparable bio-based crude oil is today 122 $ barrel (palm oil) (1), which is approximately 0.49 € per liter. This shows that even though profitability is still not achieved, it is concluded that profitability is not far away.