Electrostatic precipitator (ESP) operating envelope: select the approximate maximum gas temperature and pressure for which dust-laden streams can be effectively cleaned at very high collection efficiencies (≈99.9%).

Introduction / Context:
Electrostatic precipitators (ESPs) exploit electrostatic charging and drift to collect fine particulates from gas streams in power, cement, and metallurgical operations. Their usable temperature and pressure ranges are limited by materials, electrical breakdown characteristics, and gas properties that affect corona stability and resistivity.

Given Data / Assumptions:

• Target collection efficiency on the order of 99.9% for fine dusts.
• We consider the upper practical bounds for industrial ESPs with appropriate materials.
• Gas composition and dust resistivity are within typical controllable ranges (conditioning possible).

Concept / Approach:
ESPs are routinely applied to hot flue gases; specialized designs can handle several hundred degrees Celsius with proper electrode and insulator materials. While most operate near atmospheric pressure, ESP principles are not inherently limited to low pressure; pressure vessels and process constraints may extend the pressure envelope. Among the options provided, the pair of about 500°C and tens of atmospheres reflects the most reasonable “maximum” within the set.

Step-by-Step Solution:
Eliminate unrealistic extremes: 1000°C severely challenges electrodes/insulators and corona.Recognize typical high-temperature ESP practice near a few hundred °C; 500°C is an upper bound in the given choices.Select the associated pressure bound (50 atm) as the best available match from the list.

Verification / Alternative check:
Vendor specifications often cap continuous operation substantially below 1000°C. Engineering references cite high-temperature ESPs up to several hundred °C; pressure capability depends on housing design rather than collection physics.

Why Other Options Are Wrong:
1000°C options: impractical due to thermal and electrical constraints.200°C and 5 atm: feasible but not “maximum” envelope among the options.

Common Pitfalls:
Ignoring dust resistivity windows and gas conditioning (e.g., SO3 injection or humidification), which strongly affect capture independent of temperature/pressure limits.

Final Answer:
500°C and 50 atm