Overview

Selecting the appropriate feedwater system is a critical decision in boiler system design, directly impacting energy efficiency, operational reliability, maintenance requirements, and lifecycle cost. This document provides a comparison between pressurized deaerator systems and atmospheric feedwater systems.

• Atmospheric Feedwater System
  Open-to-atmosphere tank (0 PSIG), uses steam sparging for heating and limited O₂ removal; water temperature usually ~180–210 °F.
• Pressurized Deaerator (DA) System
  Closed vessel operating under pressure (5–15 PSIG), mechanically removes dissolved gases (O₂ and CO₂); water temperature typically ~225–235 °F (depending on pressure).

Cost Comparison

Typical DA systems can cost 2–3 times more upfront than atmospheric setups due to ASME vessel requirements and instrumentation.

Pressurized Deaerator System

Key Benefits

• Superior Oxygen & CO₂ Removal
• Meets stricter O₂ levels: <0.005 cc/L typical vs ~0.02–0.03 cc/L in atmospheric systems.
• Reduces need for high chemical scavenger doses (less sulfite).
• Higher Feedwater Temperature
• Increases boiler efficiency by reducing heat input to convert to steam.
• Minimizes thermal shock on boiler tubes.
• Better for High Pressure & High Load Applications
• Required for systems >150 PSIG or tight corrosion standards.
• Lower Corrosion Risk
• Improved protection for boilers, economizers, and steam piping.
• Potential Lower Long-Term Operating Cost
• Reduced water treatment usage, longer boiler life.

Considerations / Costs

• Higher initial capital cost due to pressure vessel design and controls.
• Increased complexity requires trained operators and maintenance personnel.
• Additional safety considerations and compliance requirements.
• Lower chemical cost but adds venting steam loss (minor heat penalty).

Atmospheric Feedwater System

Key Benefits

• Lower Capital Cost
• Attractive for budget-sensitive or small plants.
• Simpler Design and Operation
• No pressure vessel → easier installation and maintenance.
• Flexibility
• Adequate for low-pressure applications (≤150 PSIG typical).
• Lower Risk of Pressure-Related Safety Issues
• No need for ASME pressure vessel codes on the tank.

Considerations / Costs

• Lower feedwater temperatures lead to higher fuel consumption.
• Less effective oxygen removal, increasing corrosion risk.
• Needs higher levels of oxygen scavengers and pH conditioning, which increases operational cost.

Typical Application Guidance

• Atmospheric System:
  • Smaller plants, lighter duty, lower design pressures.
  • Miura EX or LX series boilers operating at 125 PSIG or below.
• Pressurized DA System:
  • Plants with high-pressure boilers (>150 PSIG).
  • Large steam loads, process critical, longevity priority.
  • Where water quality and corrosion control are strict.

Summary Comparison

Pressurized deaerators offer higher efficiency and system longevity, making them ideal for high-demand and energy-sensitive applications. Atmospheric systems provide a cost-effective solution for smaller or less critical steam systems where capital budget is a concern.

Summary Decision Framework

• If lowest CAPEX and <150 PSIG system pressure → Atmospheric Feed Tank.
• If long-term efficiency, reduced corrosion, high-pressure system (>150 PSIG), or minimal chemical dosing is a priority → Pressurized Deaerator is the better option.