The rural community still lacks access to clean, cost effective and sustainable form of energy that is needed to power their socio-economic activities, particularly for agriculture, water supply and food processing. Bioenergy is the main form of energy to rural residents particularly wood-fuel, which is mainly used for cooking. On one hand, use of wood-fuel for energy contributes negatively to deforestation and hence loss of CO₂ sink, the quality of life due to inherent indoor air pollution and overburdening women and children as a result of walking long distances to collect wood fuel [1] . On the other hand, modern renewable energy technologies such as wind and solar are relatively expensive for rural community to adapt [2] [3] . Biofuels are considered to be potential alternative source of energy that can, if properly harnessed, enhance energy access to the rural community. Liquid biofuel such as POs can be easily processed and distributed to be accessed and utilised at village level for running diesel engines.

However, POs cannot be used directly in diesel engines because of high viscosity and low volatility as well as presence of gums and free fatty acids (FFAs), which affects engine operation and durability [4] - [15] . Some research efforts [8] [16] [17] have focused on engine modification to handle high viscosity biofuel. Modifying of PO to improve fuel properties so that it can be used without modifying an engine, could be the best way of handling the problem with the main objective of enhancing direct use of PO at minimum modification.

Some of the techniques used in modifying POs are such as transesterification, pyrolysis, blending and micro- emulsion [10] . However, selection of a suitable plant oil modification process is a function of many factors. One of the factors which may influence the choice of any process in chemical engineering includes technical factors, present and future availability of raw material for sustainable production, equipment (availability, material of construction), plant location and costs [18] [19] . Technical factors are such as the complexity of the process and performance of the process in the quality of final product as well as safety. Plant location for this case, is for a process that fits the rural situation.

In most cases, rural economy is characterised by low per capita economy and therefore the main challenge is an appropriate process that can meet low capital investment and yet ensure financial return to the investor. Moreover, some methods and technologies used, still display low performance in reduction of viscosity and removal of gums and FFAs. So the main questions to answer are what reasonable quality of PO is needed for rural setting utilisation; what measures are required to improve oil quality for use as fuel in diesel engines commonly found in remote rural environment, by analysing on which methods exist can reduce the unwanted components in the PO to an acceptable level, both small-scale, simple, low cost and applicable for the rural setting.

Quite a number of PO research publications and reports, analyses and reviews are more concerned with the technical analysis and the economic feasibility (techno-economic analysis) of biodiesel production by using transesterification reaction method [6] [13] [14] [20] - [25] . However, the cost implications of modifying PO using other methods have not been a major concern. It is therefore important to conduct a techno-economic analysis of the non-transesterification method used to modify POs.

Although techno-economic analysis on biodiesel industry has been performed by several studies to date in determining its economic prospective and profitability, in all the studies it has been found that even though biodiesel is more renewable and cleaner than fossil diesel, it has relatively high production costs which makes it not economic viable due to its price. Another major observation is that costs of feedstock comprise a very substantial part of overall biodiesel cost (about 75% - 80% of the total operating costs) [23] [24] . To address these obstacles, the need to either develop technologies which allow the use of low-cost and lower value feedstock or to use viable conversion process as well as the recovery of high quality glycerol has been suggested.

This highlighted the need for a flexible model to be developed, which could aid in the comparison of alternative production routes for their abilities in reducing production costs to desirable levels and making the conversion of POs into liquid biofuel which be economically viable. The developed model could assist in determining the overall economic feasibility of a proposed operation and its flexibility could guide choices regarding feedstock, plant capacity, chemical process or conversion process and design as a whole [23] since in a simulation software, all aspects of a process are accounted for simultaneously and when changes are made to one aspect of the process, the impact on all other areas is automatically determined [26] .

This paper focuses on the modification of plant oil as a way of improving the fuel properties of jatropha (Jatropha Curcas) seed oil so that it can be used as a potential ready-to-use fuel in low- and medium-speed diesel engines for rural community without modifying an engine. These engines are commonly used in rural areas for many social economic activities. Lister engines are a good example of these engines. The main objective of this study is to evaluate techno-economic viability of a non-transesterification method or process developed to modify PO into a suitable liquid biofuel for rural setting. This involves modeling a non-existing industry based on the country’s technology capacity.

A small-scale MPO production plant that has an annual production capacity of 15,072,741 kg of MPO (batch process) was designed and simulated in SuperPro Designer. MPO production involves modifying of PO to lower and/or remove the undesired materials from PO to produce PO with fuel properties that has similar specifications of diesel fuel grade 4-D (ASTM D975), for use in low- and medium speed diesel engines. The main problems to address were viscosity, FFAs and gums (Phospholipids). Thus, the major processes involved were degumming, neutralisation and blending.

Degumming materials were water and phosphoric acid. Sodium hydroxide (NaOH) was used for neutralisation of FFAs. The blending material used was Natural Gas Condensate (NGC), which is a by-product of natural gas extraction. The condensate is supplied by Tanzania Petroleum Development Corporation (TPDC) (Dar es Salaam, Tanzania) from Songosongo gas fields. The composition of the Songosongo natural gas condensate was as shown in Table 1 as per [27] and [28] . The condensate was water-free with the composition of FFAs of only about 0.01% w/w.

Figure 1 shows the simulation of the entire MPO production process starting from crude jatropha oil (JO) as the feedstock specified to MPO (or modified JO) as the main product. Process simulation with SuperPro Designer software allows predicting the behaviour of a process using basic engineering relationships such as mass and energy balances, phase equilibrium and kinetics reactions. With reliable thermodynamic data, realistic operating conditions and the rigorous SuperPro Designer equipment models, the software was able to simulate the perfor- mance of an actual MPO industrial plant.

SuperPro Designer can help design better plants or process within existing plants to help increase profitability. Due to its flexibility, the software allowed interactively change of specifications such as operating conditions, flowsheet configuration and feed compositions to run new cases and analyse alternatives. SuperPro Designer is the only commercial process simulator that can handle equally well batch and continuous processes as well as combination of batch and continuous processes. More importantly, it has modelling capabilities which are suitable for this application [18] [26] [29] - [32] .

The simulator includes mathematical models that perform cost analysis and project evaluation calculations. The project feasibility was assessed based on the Net Present Value (NPV) or Net Present Worth (NPW) profitability indicator. NPV can be defined as the difference amount between the sums of discounted: cash inflows and cash outflows; or the difference between total present value of annual cash flows and the total capital investment. It is a standard method for using the time value of money to appraise long-term projects [18] - [20] .

The results of simulation were presented in the form of reports which were generated and saved in a temporary file in the SuperPro Designer. They were then exported to a Microsoft Excel 2007 for ease of access. There are several reports generated; each focusing on a different topic. However, only Economic Evaluation Report (EER)

and Throughput Analysis Report (THR) were presented in this paper, which provided mass balances, energy balances and economic evaluation results.

Sensitivity analysis results showed the impact of changing specifications such as operating conditions, flowsheet configuration and feed compositions. The two new cases or scenarios were analysed as alternatives: First scenario: the impact of feedstock price fluctuations on MPO predicted price using the process model simulated pro-

ducing 15,072,741 kg of MPO annually. Second scenario: the predicted unit cost of producing MPO of the adjusted annual production. This scenario simulated the impact of plant capacity to economic feasibility of MPO production.

From Techno-economic analysis performed, the total capital investment of a plant with annual production capa- city of 15,072,741 kg of MPO is about US $ 10,222,000 (or US $ 10.2 M) with a PBP of 1.7 years and the pre- dicted unit production cost of MPO is US $ 1.315/kg at a value of US $ 1.0/kg of JO. The economic feasibility of MPO production is found to be influenced mainly by the price of feedstock, which contributes about 95% of the total annual production cost. Others are plant capacity, price of the product (MPO) and the conversion route used. These results are consistent with the results presented from other analyses on liquid biofuel production. The analysis indicates that the process technology simulated is economically viable and can be implemented in rural setting, taking into consideration Tanzania’s rural situation. The simulated model is flexible in terms of scale and process. Alternative scale or process pathways can be easily introduced to modify and assess the impacts for example that changes can have on capital and production costs. The multiple results available can then be used to find those scenarios or production systems that exhibit better performance. It also serves as the basis for future work with different POs or feedstocks. SuperPro Designer analytical tool enables a wide range of pro- cess configurations that are adapted to meet Tanzania’s conditions to be simulated within a short time.

The Authors acknowledge the financial support provided by the Policy Innovation Systems for Clean Energy

Security (PISCES) research project, which was a five-year initiative project funded by the UK’s Department for International Development (DFID). PISCES which had partners in Kenya, India, Sri Lanka, United Kingdom and Tanzania was intended to provide policymakers with information and approaches that they can apply to unlock the potential of bioenergy to improve energy access and livelihoods in poor communities. The Authors also acknowledge the Department of Chemical and Mining Engineering, University of Dar es Salaam for their co-support in this work as well as Tanzania Petroleum Development Corporation (TPDC) for supplying the natural gas condensate (NGC).