To reduce stack (exhaust) heat losses from an industrial furnace, which heat-recovery strategies are appropriate?

Introduction / Context:Stack losses represent sensible heat carried away by hot flue gases. Capturing part of this energy lowers fuel consumption and improves thermal efficiency in furnaces and kilns.

Given Data / Assumptions:

• Flue-gas temperature is above the practical recovery threshold without causing corrosion/condensation issues.
• Suitable heat-recovery hardware is available.

Concept / Approach:Three proven strategies: (1) Preheat the charge via recuperative/regen systems or indirect exchangers; (2) Preheat combustion air to raise adiabatic flame temperature; (3) Generate steam via a waste-heat boiler for use elsewhere in the plant.

Step-by-Step Solution:Quantify recoverable heat: Q = m_dot * Cp * (T_stack - T_exit).Select utilization path matching process needs: charge, air, or steam.Implement control and corrosion safeguards (e.g., maintain temperatures above acid dew point if not designed for condensing service).

Verification / Alternative check:Energy audits typically identify these three avenues as primary opportunities for stack-loss reduction.

Why Other Options Are Wrong:Each option is valid; picking only one underutilizes potential recovery.

Common Pitfalls:Ignoring fouling/soot deposition in exchangers; failing to account for increased pressure drop across recovery equipment.

Final Answer:all (a), (b) and (c)