11 replies to this topic

[addiesalsabil]

Hi,
 

I'm currently designing the utility unit of a plant, specifically on the power generation with steam turbine. I was recommended to have boiler that generates superheated steam that will be fed to the steam turbine. The output steam (assumed already in saturated steam) from the turbine will be used in the process for heating etc.

 

The question is, how do I know how much superheated steam needed to be converted to saturated steam to fulfil the process demand? I'll be using superheated steam at 260°C and the saturated steam in the process is 174°C.

 

Could you provide me with insights and resources? Any help would be much appreciated.

 

Kind regards,

Addie

Edited by addiesalsabil, 10 September 2023 - 10:28 AM.

[Bobby Strain]

Gas turbines don't usually require steam.

 

Bobby

[addiesalsabil]

I'm sorry, my bad. What I meant is steam turbine

[Bobby Strain]

The usual practice is to extract steam from the turbine for process needs.

 

Bobby

[fallah]

 

I'm currently designing the utility unit of a plant, specifically on the power generation with steam turbine. I was recommended to have boiler that generates superheated steam that will be fed to the steam turbine. The output steam (assumed already in saturated steam) from the turbine will be used in the process for heating etc.

 

The question is, how do I know how much superheated steam needed to be converted to saturated steam to fulfil the process demand? I'll be using superheated steam at 260°C and the saturated steam in the process is 174°C.

 

Could you provide me with insights and resources? Any help would be much appreciated.

 

 

Hi,

 

You have to do a steam balance for your plant to achieve the required steam in all levels i.e. LLP steam, LP steam, MP steam, HP steam and VHP steam. Then for running the steam turbine you have to use high pressure super heated steam which is to be converted to high pressure saturated steam after passing through the turbine which can be used as part of required HP steam to fulfill the process demand.

 

The super heated steam can also be converted to saturated steam by using desuperheater...

[breizh]

Hi,

Consider this link to support your study. Let you dig into it.

 

A set of calculators with examples.

https://www4.eere.en...amo_steam_tool/

 

edit:

doc attached: true cost of steam .

 

Good luck

Breizh

[Pilesar]

Even though you say the process needs saturated steam, the steam is usually kept superheated for transport in piping to the end user. Some heat will be lost during the transport and you typically want to have dry steam at the end user. Dry steam is easier to measure and control and doesn't cause hammering problems. A small amount of superheat in steam (25 C or so) when used for process heating doesn't help much and doesn't hurt much either so it is usually still considered 'saturated steam' in practice even with a little superheat. As the utility unit designer, you cannot dictate how much saturated steam the plant needs. The plant unit designers must tell this number to the utility unit designer. The steam turbine can be designed to exhaust steam at the pressure required for the process. Steam balances can be tricky since flexibility adds cost. If you must design the utility unit without a firm design basis, you may want to make the system larger than you think will be needed and plan to sell the extra electricity into the grid outside the plant.

[Bobby Strain]

Maybe you should start from the beginning, as Pilesar has suggested.

 

Bobby

[addiesalsabil]

I appreciate the help, thank you everyone

[fallah]

It is almost impossible to optimize required steam and condensate system of a plant without a steam balance, because it requires a complete understanding of the system. The easiest and best method to deliver that steam system understanding is to create a steam balance flow diagram.

 

A perfect steam balance between steam generation, distribution, end-users (steam turbines, heat exchangers, reboilers,...) requirements, and condensate recovery can (and should) be performed by utility unit designer provided that all end-users information about required steam consumptions had already been provided by plant unit designer.

[theangkko]

To provide process steam from a steam turbine, it is difficult to control the extraction steam "flow" within the power plant process. Typically, the extraction steam "pressure" is fixed for utilities. Maintaining pressure implies that the required amount is provided regardless of usage.

 

For example, having 10 donuts always ready in a display case suggests a stable supply, no matter how many customers come. However, the steam turbine has a set mass flow it can provide. Excessive extraction of steam can lead to operational limits considering internal steam velocity and cooling.

 

Therefore, factories receiving steam should calculate the minimum and maximum required steam flow for each operational case by preparing mass and heat balances

[EnggExp]

To calculate how much superheated steam you need to generate, you’ll need to perform a steam and energy balance around the steam turbine and the process system.
1. Define Process Heating Load
• Determine the total thermal energy required in the process, say in kW or kg/h of saturated steam at 174°C.
• For example, suppose the process requires 10,000 kg/h of saturated steam at 174°C (corresponds to ~8.6 barg).


2. Select Steam Turbine Inlet & Outlet Conditions
• Inlet: Superheated steam at 260°C (say at 45 barg)
• Outlet: Saturated steam at 174°C (say at 8.6 barg)

Use steam tables to get specific enthalpies:
• At 45 barg & 260°C: h_{\text{in}} \approx 2960 \, \text{kJ/kg}
• At 8.6 barg, saturated: h_{\text{out}} \approx 2780 \, \text{kJ/kg}

So, turbine work output per kg of steam:
W_{\text{turbine}} = h_{\text{in}} - h_{\text{out}} = 2960 - 2780 = 180 \, \text{kJ/kg}

3. Match Mass Flow
• If the process needs 10,000 kg/h of saturated steam, and if the turbine exhaust steam is all recoverable and at the right condition, then:

10,000 kg/h of superheated steam input = 10,000 kg/h of turbine exhaust steam output
(assuming no steam is lost in the turbine)

So, your boiler needs to produce 10,000 kg/h of superheated steam at 260°C.

Optional Refinements:

If you want to:
• Extract more power, use more superheat or expand to lower pressure.
• Handle partial extraction, split turbine exhaust (some for process, some to condenser).
• Model efficiency, assume an isentropic efficiency (e.g., 80%) for turbine and recalculate actual power generated.