Coal washeries — The calorific value of coal middlings produced during coal washing is typically around how many kilocalories per kilogram (kcal/kg)?

Introduction:
Coal washing separates run-of-mine coal into clean coal, middlings, and rejects. Middlings are often used as a lower-grade fuel for captive power or industrial boilers, so knowing their approximate calorific value is important for utilization planning.

Given Data / Assumptions:

• Middlings are intermediate-density fractions with higher ash than clean coal but lower than rejects.
• Typical Indian washeries and similar operations are implied.

Concept / Approach:
As ash content increases, calorific value decreases. Clean thermal coal may be 5000–6500 kcal/kg; middlings tend to be in the mid-range (often around ~3500–4500 kcal/kg), while rejects can be much lower.

Step-by-Step Solution:
Recognise middlings as mid-quality fraction.Recall typical CV range for middlings ≈ 3500–4500 kcal/kg.Select the closest listed representative value: 4000 kcal/kg.

Verification / Alternative check:
Power plant fuel-blending practices and washery reports often list middlings near this value, adjusting for local geology and washery cut-points.

Why Other Options Are Wrong:

• 1000 and 2500: Too low; characteristic of high-ash rejects.
• 6000 and 8000: Too high for middlings; in the range of cleaned coal or premium grades.

Common Pitfalls:
Assuming middlings are nearly as good as clean coal; ignoring site-specific ash and moisture variations that shift CV by several hundred kcal/kg.

Final Answer:
4000