5 replies to this topic

[anilpagar]

Dear Friends,

I am trying to design bonnet for 1200 °C (Hot smoke gas) for high temperature application.

what I have done is as below.

1. I have calculated the Q for the valve body
2. Compare with cermaic packing Q & found length out of the same.

Q body = 2 pi k L (To-Ta) / ln (r2/ri)

L = Q body * ln (r2/r1) / 2 pi k L (T0-Ta)

Is this right ?

How shall I design my bonnet. How shall I take heat transfer co-efficient.

Kindly share your experience with such application. Your guidance will be required to calculate heat loss from body and bonnet.


Best Regards

Anil Pagar

[Art Montemayor]

Anil:

I don’t think you have given sufficient basic data for members to accurately comment on your topic:

• Although you don’t state it, I believe you are dealing with a process line block valve that has hot, 1200 °C, gas flowing through it and you need to insulate its bonnet.
• What type (or kind) of block valve are you dealing with?
• Why are you designing the valve bonnet? Wasn’t the valve selected in accordance with an existing valve specification for the service?
• What are the process design conditions on the valve?
• What is the size of the valve and how is it installed?
• Please furnish a detailed, dimensioned drawing of the valve and a photograph (if possible).

What you are confronting is no different from what I and many other engineers have had to confront in the field when processing high-temperature and cryogenic fluids. I have simply extended the length of the bonnet (or “Stem”) on the valve. It all depends on the specific, type, design, and fabrication of the subject valve. When you extend the stem of the valve (which can be done integrally or externally) you create a static gas barrier between the process gases flowing within the body of the valve and the external parts that are subject to human contact – such as the valve handle. There is no better insulation than a static volume of gas. The thermal conductivity through the static gas is so low that any heat conduction through it is negligible and the external parts of the valve such as the stem and handle can be easily touched since they are maintained as essentially ambient temperature.

But before going any further into this application, the Forum needs the basic data listed above in order to establish and verify what you are doing and on “WHAT”.

Await your response.

[anilpagar]

Hello Admin,

Thank you very much for your reply & sorry for the late reply. I have worked on this application and design is in process.
Still I will like to know your view as such applications are very critical.

I have used the extended bonnet and also added the fins on this bonnet. We have very less information regarding flow media.

• Although you don’t state it, I believe you are dealing with a process line block valve that has hot, 1200 °C, gas flowing through it and you need to insulate its bonnet.

This application is for carbon black manufacture. This valve will be mounted on exhaust side. As customer has given very few details.

• What type (or kind) of block valve are you dealing with?

We are using butterfly valve

• Why are you designing the valve bonnet? Wasn’t the valve selected in accordance with an existing valve specification for the service?

Since this valve is for high temperatures & we never made such valve , we tried to calculate length to make sure that we have selected proper length.

• What are the process design conditions on the valve?

Flow rate will be around 400 Nm^3 / hr - 900 Nm^3/hr. Pressure will be 1 kg/cm^2

• What is the size of the valve and how is it installed?

size of valve is DN 200 (8") butterfly valve.

• Please furnish a detailed, dimensioned drawing of the valve and a photograph (if possible).

It will be little difficult to furnish any drawing & photograph is not possible as product is still in manufacturing.

Also please tell me more about the better insulation than a static volume of gas & how this will work as insulator.

Thank you very much sharing knowledge.

Best Regards

Anil Pagar

[Art Montemayor]

Anil:

I believe I already told you enough information to allow you start – or complete – a mechanical design on a valve extended stem:

“When you extend the stem of the valve (which can be done integrally or externally) you create a static gas barrier between the process gases flowing within the body of the valve and the external parts that are subject to human contact – such as the valve handle. There is no better insulation than a static volume of gas. The thermal conductivity through the static gas is so low that any heat conduction through it is negligible and the external parts of the valve such as the stem and handle can be easily touched since they are maintained as essentially ambient temperature.”

When you extend the valve stem, always guide and support the extended stem internally. I think this is well-understood and should follow common sense. Design the extended stem so that you create one - or more – “dead air” cavities within the length of the stem. What these cavities do is to trap air and keep it static. If you are an engineer, you should know that gases or vapors have very poor thermal conductivity values and are, essentially, insulators of the first degree. Air pockets in their fur is what keeps polar bears snug and warm in arctic winters. The same effect applies elsewhere.

[anilpagar]

Hello Admin,

thank you very much for inputs ans valuable information.

We have designed the shaft and support the same in Bonnet. Keeping in mind Air works as insulator we have created three cavities for air gap or static gas.

Hope I will be able to share the picture & corss section with you once valve is completed.

Best Regards

Anil Pagar

[anilpagar]

Hello admin,

With reference to above subject I got below information from web. Kindly go through the same. Is this method for calculation is correct ? can we apply he same method for calculation of bonnet.

http://instrumentation.web.id/?p=886

Looking forward for your reply.

Best Regards

Anil Pagar