Deaerator Design and Operation Report Making Help

[Pavan Kumar]

Hi All,

I am writing a report to share Knowledge about Design and Operation of Deaerators. I have gone through some very insightful threads in this forum on this topic such as the one shown below. I know there are two types of Deaerators

(i) Spray Type
(ii) Tray Type

https://www.eng-tips.com/viewthread.cfm?qid=103577

Since I am making schematic drawings for each type of Deaerator and describe how it operates in detail, the maximum turn down ratio it can operate at, advantages, cost and installation considerations. I need some help with references in this regard. For the process design aspect I am using the following link from Spirax Sarco and will do an example calculation to illustrate the design. I think the calculation illustrated in this link are good for atmospheric design too.

https://www.spiraxsarco.com/learn-about-steam/the-boiler-house/pressurised-deaerators?sc_lang=en-GB

In particular I am not clear about how exactly a Horizontal Spray Type Deaerator performs a good deaeration operation. I understand there is Spray Nozzle that sprays water into the Pre-Heating and Partial Deaeration section where it contacts with the Steam rising from the sparger pipe.

1. This is like steam contacting a fine mist. My question is does this provide enough contact area like in the Counter Flow Tray Type Deaerator.
2. The partially deaerated water then flows across the baffle into the Deaeration section where the water is heated with steam bubbling from the sparger pipe with sparger holes at the bottom of the tank. Is this baffle all the way to the bottom so that the water has to flow over it to get to the Deaeration section?
3. Now again with steam bubbling like this how does it get good contact area to thoroughly scrub and deaerate the water.
4. I know Spray Deaerators also Deaerate up to 7 ppb O2 requirement and are used when it is operated at the Design Load. How does the steam sparger design effect the Deaeration operation and how does it adjust with the variation in the loads?.
5. Is the steam flow regulated by the operating temperature in the tank?.
6. In case of Tray type of Deaerator is the steam flow regulated by the temperature of the deaerated water in the storage section?.

I also see that there is a Vertical Spray Type Deaerator also. I have seen on the Kansas City Deaerator website. I want to understand this with sketches and to illustrate.

https://deaerator.com/deaerator-products/standard-spray-deaerators/vertical-spray-deaerator/

Thanks and Regards,
Pavan Kumar

 

[FacEngrPE]

1. All good deareators are counterflow. First steam must heat the drops, inward flow of condensing steam will prevent difusion of non condensibles. Once the drop is heated to steam temperature, noncondensible gas can difuse out of the drops. Smaller drops have less distance for the gas to difuse through, so less time at temperature is required for smaller drops, and the more surface area.

2. All (most?) of the deareation occurs while the water is in small drops, being scrubbed by steam at the same temperature as the drop. No deareation can occur while the steam is heating the drops, as steam will be condensing on the outside of the drops. Baffles increase contact time. The the storage section serves as a reservoir of hot water so it is a consideration when selecting other components of your boiler system (particularly where do you want your storage).

3. I would not consider the sparger to do much in the way of deareation, it does keep the storage section hot so it will retain the degassed condition. Spargers are a necessity on DA's with large sumps. DA's with small sumps do not need spargers, the steam can be added above the high waterline.

4. A properly operating deareator should be able to provide 3 ppm O2. Smaller drops / more surface area / better deareation.

5. Tank temperature must be constant. Temperature is controlled by providing a well regulated constant pressure steam supply.

6. No. It is enough to ensure the pressure in the shell is constant,

Spray type must be used in marine applications, as tray type only works correctly when the trays are level.

You should be aware that deareator service is very abusive due to the operating conditions.

• Pressure upsets will result in significant water hammer, and will disrupt the deareation process.
• Do not use material subject to chloride stress corrosion cracking.
• Follow the inspection recommendations of the National Board (or your local AHJ.)

I have read both of your citatations, both are reputable. Don't rely on just manufactures information, the following documents are recomended reading.

EPRI has published Deaerator Tank Assessment Guideline - EPRI

The National Board of Boiler and Pressure Vessel Inspectors published System Design, Specifications, Operation, and Inspection of Deaerators​