2.2.2. Estimation of Cost and Revenue

The cost component was made up of the investment cost and cost of operation and maintenance. The investment cost consisted of all the expenses required to set up the complete drying system. This included the cost associated with the fabrication of the drying column, biomass burner, and an electric blower. The cost of electricity for operating the drying system during operation and a flat rate of 2% of equipment and machinery cost was assumed to be operation and maintenance costs, respectively. The cost of fuel, which comprised of the cost of corn cobs, was not considered since the biomass residue is anticipated to be readily available in the study area. The revenue generation stream was sourced from the price charged for providing drying services to other farmers in the community. The drying charge and quantity of maize anticipated to be dried were presented in the economic model to determine the annual total revenue generated.

#### 2.2.3. Economic Appraisal

Net Present Value (NPV), Internal Rate of Return (IRR), Benefit-Cost Ratio (BCR), and Payback Period were used to evaluate the economic performance of the column dryer.

NPV uses a discounting method for evaluating the economic viability of the investment and gives the value of all future cash flows in today's currency. This provides a true measure of an investment's economic feasibility. It presents the present value of cash in and outflows [14]. A positive NPV indicates an economically viable investment or project, while a negative one shows that it is not economically feasible to carry out such investment or project [15]. Equation (5) was used to calculate the NPV.

$$NPV = \sum\_{t=0}^{N} a\_t S\_t \tag{5}$$

where *St* = net cash flow at a specific time (*t*), *N* = number of years (10 years), and *at* = financial discount factor, which was calculated using Equation (6).

$$n\_t = \frac{1}{\left(1+i\right)^t} \tag{6}$$

where *t* = time from 0 and 10 years and *i* = the discount rate (%).

IRR is the discount rate that makes the net present value of all cash flows from a particular investment equal to zero. Generally, the higher the IRR, the more desirable it is to undertake the project [16]. IRR was determined using Equation (7).

$$NPV = \sum \frac{S\_t}{(1 + IRR)^t} = 0\tag{7}$$

PBP is the number of years it takes to recover an investment's initial cost. It provides a simple way to assess the economic merit of investments. Equation (8) was used to calculate the PBP.

$$PBP = \frac{C\_i}{S} \tag{8}$$

where *Ci* = initial investment cost and *S* = net cash flow

*BCR* is the ratio of total discounted benefit to total discounted cost. Projects with a benefit-cost ratio greater than 1 have greater benefits than costs; hence, they have positive net benefits. The higher the ratio, the greater the benefits relative to the costs. It was calculated using Equation (9) [17].

$$BCR = \sum \left( ^{B\_l} / (1 + d)^i \right) \stackrel{\star}{\twoheadrightarrow} \sum \left( ^{\odot\_l} / (1 + d)^i \right) \tag{9}$$

where *Bi* = benefit of the project in year *i* (*i* = 0 to 10 years), *Ci* = cost of the project in year *i*, and *d* = discount rate.

2.2.4. Financial Assumptions

The following financial assumptions were made during the assessment:

