Question

A city generates on average 1000 metric tonnes/day (t/d) of municipal solid waste and follows an integrated waste management system. 15% of the total waste is recycled, 40% used to produce compost, 25% converted to refuse derived fuel (RDF) with 80% efficiency, and the remaining disposed in a sanitary landfill. The calorific value of the RDF is 15 MJ/kg. The electrical energy that could be generated from the RDF with a thermal-to-electrical conversion efficiency of 20% is ____________________ (in MWh/d, rounded off to two decimal places).

Hint:

Track mass splits first, then apply heating value and efficiencies. Remember the handy conversion: $1\ \text{MWh}=3.6\times10^3\ \text{MJ}$.

Answer 1

Correct Answer: 165

Step 1: Mass of waste routed to RDF.
Fraction to RDF $=25%$ of 1000 t/d $\Rightarrow 250$ t/d of feed to the RDF process.
Process efficiency $=80%$ $\Rightarrow$ RDF actually produced $=0.80\times 250=200$ t/d.
\[ 200\ \text{t/d}=200{,}000\ \text{kg/d}. \]
Step 2: Daily thermal energy in the RDF.
\[ E_{\text{thermal}}= \text{mass}\times \text{CV}=200{,}000\ \text{kg/d}\times 15\ \text{MJ/kg}=3{,}000{,}000\ \text{MJ/d}. \]
Step 3: Convert thermal energy to electrical energy (20% efficiency).
\[ E_{\text{elec}}=0.20\times 3{,}000{,}000=600{,}000\ \text{MJ/d}. \]
Step 4: Convert MJ to MWh.
$1\ \text{kWh}=3.6\ \text{MJ}\Rightarrow 1\ \text{MWh}=3600\ \text{MJ}$. Hence, \[ E_{\text{elec}}=\frac{600{,}000\ \text{MJ/d}}{3.6\ \text{MJ/kWh}}=166{,}666.7\ \text{kWh/d}=166.67\ \text{MWh/d}. \] Final Answer: \[ \boxed{166.67\ \text{MWh/d}} \]