Bag filter (fabric filter) design: why is gas temperature a critical input for design and operation?

Introduction / Context:
Fabric filters (baghouses) capture particulate by passing dirty gas through a porous medium. Gas temperature strongly influences both the fluid-dynamic behavior of the gas–dust mixture and the durability and suitability of filter media. Designers use temperature to set allowable operating windows and to prevent bag damage or condensation.

Given Data / Assumptions:

• Normal dry filtration with pulse-jet or shaker cleaning.
• No chemical degradation beyond temperature-driven effects.
• Gas composition does not change temperature significantly across the filter.

Concept / Approach:
First, temperature affects gas density (ρ) and viscosity (μ), and thus Reynolds number and pressure drop through the filter cake and fabric. Second, filter fibers have maximum continuous service temperatures; exceeding these can shrink, embrittle, or melt media (e.g., polyester vs. PPS vs. PTFE). Finally, temperature impacts dew point margins; operating near or below acid dew points causes condensation and cake blinding or corrosion.

Step-by-Step Solution:

Verification / Alternative check:
Empirical correlations for filter resistance include μ and cake properties; vendor datasheets list maximum continuous temperatures for each fabric, confirming temperature’s central role.

Why Other Options Are Wrong:

• (a), (b), (c) each capture only part of the influence; the complete and correct choice is that all apply.

Common Pitfalls:
Ignoring acid dew point and focusing only on media softening temperature. Both upper and lower temperature limits matter for reliable, low-maintenance operation.

Final Answer:
All of (a), (b) and (c)