Why is turndown ratio important in equipment design?

Turndown ratio is the ratio of maximum to minimum operating capacity. Important because: Operating flexibility - plants rarely run at exactly design capacity. Startup/shutdown - need to operate at low rates. Market variations - adjust production to demand. Process stability - maintain control at reduced rates. Equipment considerations: Heat exchangers - reduced flow affects velocity and fouling. Distillation - trays may weep, packing may maldistribute. Pumps - minimum flow to prevent damage. Control valves - sized for rangeability, typically 50:1. Compressors - surge limits minimum flow. Furnaces - minimum firing for stable combustion. Design practice: specify turndown requirement (typically 50-70% of design), verify equipment operates satisfactorily, and include recirculation or spillback where needed.