Process Boiler #2 Automatic Blowdown & Deaerator Settings
Measure Overview
This proposal would add the following requirements for all newly installed process steam boiler systems with capacities at or above 10 MMBtu/h:
- The boilers have an automatic surface blowdown controller that is programmed to be controlled by conductivity, and
- For systems that use the boiler steam header to pressurize the deaerator, the steam supply line pressure regulator serving the deaerator must be set at or under 5 pounds per square inch of gauge pressure (psig) and between 2 and 5 psig for boilers with tubes not rated for oxidizing conditions.
The requirement would apply to all sites with new process steam boilers, including replacement boilers and boilers in additions to existing facilities, with the following exceptions:
Exceptions for the automatic blowdown requirement:
- Boiler systems with returned condensate composing more than 90 percent of feedwater flow,
- Boilers with make-up water treated by a reverse osmosis system, and
- Boilers with a heat exchanger that recovers energy from the blowdown to heat make-up water or another process stream, with or without a flash tank (blowdown heat recovery).
Exception for the steam supply line pressure regulator requirement:
- Sites with swings in make-up water equal to or above 20 percent of feedwater flow.
This proposal would require updates to compliance documents and a verification of blowdown controls, deaerator control settings, and qualification for applicable exceptions by a field technician.
Boilers used in oilfield production and utility and municipal power generation are not expected to be within the scope of Title 24, Part 6.
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Scope of Proposed Code Change
| Building Type(s) | Construction Type(s) | Type of Change | Updates to Compliance Software | Third Party Verification |
| Nonresidential | New construction, additions, alterations | Mandatory | No updates | No changes to third party verification |
Justification for Proposed Change
High conductivity in boiler water indicates high mineral content, which leads to fouling of the boiler heat exchanger tubes, increased thermal stress, and lower boiler efficiency. In addition, high dissolved solids concentrations can lead to foaming and carryover of boiler water into the steam, which can foul downstream components, trigger water hammer, and accelerate system wear and tear. To limit the levels of suspended and dissolved solids in steam boilers, water is periodically or continuously discharged or “blown down.” This surface blowdown removes dissolved solids that accumulate near the surface of the boiler water.
Given that blowdown discharges hot water, it also results in fuel, water, and chemical losses. Manual boiler blowdown is typically excessive, resulting in unnecessary losses. Automatic blowdown systems avoid excessive blowdown by monitoring and maintaining water conductivity within manufacturer-specified setpoints. This eliminates the need for operators to make manual valve adjustments and offers the following benefits:
- Fuel, water, and chemical savings
- Improved conductivity control which can extend boiler useful life and slow efficiency degradation
A deaerator is a pressurized vessel that removes dissolved air from steam boiler feedwater to protect the system from corrosion and ensure high heat transfer rates. Deaerators heat the feedwater to temperatures that release the dissolved gases (mainly O2 and CO2) from the water and are present in nearly all large boiler systems. At higher pressures, water boils at a higher temperature, so higher pressure setpoints heat the feedwater to higher temperatures, using more energy. As pressures increase, more dissolved gases are removed. A higher deaerator pressure provides a greater margin of assurance for removing dissolved gases but also results in greater steam losses.
Deaerators may be operated at higher-than-necessary pressures. Over-pressurization leads to excess venting, while under-pressurization can lead to insufficient air removal that may result in oxygen pitting and corrosion on contact surfaces. Ensuring proper deaerator pressurization through the steam supply line regulator saves energy and has no additional cost for end users.
Preliminary savings calculations and assumptions can be found in the blowdown and deaerator pressure savings calculations document. In addition to the energy benefits, these practices would reduce local photochemical smog and improve air quality. The value of improved air quality is amplified by the consideration that many industrial facilities are located near Low- and Moderate-Income (LMI) housing, which is disproportionately exposed to lower air quality.
Relevant Documents
CASE Reports
Round Two Utility-Sponsored Stakeholder Meeting Materials
Round One Utility-Sponsored Stakeholder Meeting Materials
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The Statewide CASE Team values input from all stakeholders engaged in the Title 24, Part 6 code change process. We encourage the open exchange of code change comments and concerns.