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# Steam Heating Processes - Load Calculating

## Calculating the amount of steam in non-flow batch and continuous flow heating processes.

In general steam heating is used to

• change a product or fluid temperature
• maintain a product or fluid temperature

A benefit with steam is the large amount of heat energy that can be transferred. The energy released when steam condenses to water is in the range 2000 - 2250 kJ/kg (depending on the pressure) - compared to water with 80 - 120 kJ/kg (with temperature difference 20 - 30 oC).

### Changing Product Temperature - Heating up the Product with Steam

The amount of heat required to raise the temperature of a substance can be expressed as:

Q = m cp dT                                       (1)

where

Q = quantity of energy or heat (kJ)

m = mass of substance (kg)

cp = specific heat of substance (kJ/kg oC ) - Material properties and heat capacities common materials

dT = temperature rise of substance (oC)

Imperial Units? - Check the Units Converter!

This equation can be used to determine a total amount of heat energy for the whole process, but it does not take into account the rate of heat transfer which is:

• amount of heat energy transferred per unit time

In non-flow type applications a fixed mass or a single batch of product is heated. In flow type applications the product or fluid is heated when it constantly flows over a heat transfer surface.

### Non-flow or Batch Heating

In non-flow type applications the process fluid is kept as a single batch within a tank or vessel. A steam coil or a steam jacket heats the fluid from a low to a high temperature.

The mean rate of heat transfer for such applications can be expressed as:

P = m cp dT / t                                       (2)

where

P = mean heat transfer rate or power (kW (kJ/s))

m = mass of the product (kg)

cp = specific heat of the product (kJ/kg.oC) - Material properties and heat capacities common materials

dT = Change in temperature of the fluid (oC)

t = total time over which the heating process occurs (seconds)

#### Example - Time required to Heat up Water with direct Injection of Steam

The time required to heat 75 kg of water (cp = 4.2 kJ/kgoC) from  temperature 20oC to 75oC with steam produced from a boiler with capacity 200 kW (kJ/s) can be calculated by transforming eq. 2 to

t = m cp dT / P

= (75 kg) (4.2 kJ/kgoC) ((75 oC) - (20 oC)) / (200 kJ/s)

= 86 s

Note! - when steam is injected directly to the water all the steam condenses to water and all the energy from the steam is transferred instantly.

When heating through a heat exchanger - the heat transfer coefficient and temperature difference between the steam and the heated fluid matters. Increasing steam pressure increases temperature - and increases heat transfer. Heat up time is decreased.

Overall steam consumption may increase - due to higher heat loss, or decrease - due to to shorter heat up time, depending on the configuration of the actual system.

### Flow or Continuous Heating Processes

In heat exchangers the product or fluid flow is continuously heated.

A benefit with steam is homogeneous heat surface temperatures since temperatures on heat surfaces depends on steam pressure.

The mean heat transfer can be expressed as

P = cp dT m / t                                   (3)

where

P = mean heat transfer rate (kW (kJ/s))

m / t = mass flow rate of the product (kg/s)

cp = specific heat of the product (kJ/kg.oC)

dT = change in fluid temperature (oC)

### Calculating the Amount of Steam

If we know the heat transfer rate - the amount of steam can be calculated:

ms = P / he                                       (4)

where

ms = mass of steam (kg/s)

P = calculated heat transfer (kW)

he = evaporation energy of the steam (kJ/kg)

The evaporation energy at different steam pressures can be found in the Steam Table with SI Units or in the Steam Table with Imperial Units.

### Example - Batch Heating with Steam

A quantity of water is heated with steam of 5 bar (6 bar abs) from a temperature of 35 oC to 100 oC over a period of 20 minutes (1200 seconds). The mass of water is 50 kg and the specific heat of water is 4.19 kJ/kg.oC.

Heat transfer rate:

P = (50 kg) (4.19 kJ/kg oC) ((100 oC) - (35 oC)) / (1200 s)

= 11.35 kW

Amount of steam:

ms = (11.35 kW) / (2085 kJ/kg)

= 0.0055 kg/s

= 19.6 kg/h

### Example - Continuously Heating by Steam

Water flowing at a constant rate of 3 l/s is heated from 10 oC to 60 oC with steam at 8 bar (9 bar abs).

The heat flow rate can be expressed as:

P = (4.19 kJ/kg.oC) ((60 oC) - (10 oC)) (3 l/s) (1 kg/l)

= 628.5 kW

The steam flow rate can be expressed as:

ms = (628.5 kW) / (2030 kJ/kg)

= 0.31 kg/s

= 1115 kg/h

## Related Topics

• ### Heat Loss and Insulation

Steam and condensate pipes - heat loss uninsulated and insulated pipes, insulation thickness and more.
• ### Pipe Sizing

Sizing of steam and condensate pipe lines - pressure loss, recommended velocity, capacity and more.
• ### Steam and Condensate

Steam & condensate systems- properties, capacities, pipe sizing, systems configuration and more.
• ### Thermodynamics

Thermodynamics of steam and condensate systems.

## Related Documents

• ### Air - Humidifying by Adding Steam or Water

Air can be humidified by adding water or steam.
• ### Air - Humidifying with Steam - Imperial Units

Estimate the amount of steam required (lb/h in 100 cfm) in humid air.
• ### Air and Steam Mixtures

Air in the steam will lower the surface temperatures in heat exchangers - and less heat will be transferred.
• ### Air Heating Systems

Air heating buildings - heat supply vs. air flow and temperature.
• ### ASME - International Boiler and Pressure Vessel Code

The International Boiler and Pressure Vessel Code safety rules governing design, fabrication, and inspection of boilers and pressure vessels, and nuclear power plant components during construction.
• ### Boiler Capacities

Steam boilers output can be expressed in Boiler Horsepower, MBTU or in Pounds of Steam delivered per hour.
• ### Condensate Generated in Cold Steam Pipes - Sizing of Steam Traps

When cold steam pipes are heated up they generate huge amounts of condensate that must be drained away from the pipe through steam traps - in Imperial Units.
• ### Condensation of Steam - Heat Transfer

Heat transfer when steam condensates.
• ### Cooling and Heating Equations

Latent and sensible cooling and heating equations - imperial units.
• ### Energy Transfer Equation

Fluid energy transfer.
• ### Heating Systems - Steam and Condensate Loads

Calculating steam and condensate loads in steam heated systems.
• ### Heating Up Applications - Energy Required and Heat Transfer Rates

Energy required to heat up a substance.
• ### Heating Water by Injecting Steam

Water can be heated by injecting steam.
• ### Insulated Steam Pipes - Condensate Generated

Heat loss from steam pipes generates condensate which must be drained from the system - imperial units.
• ### Sizing Steam Pipes (kg/h)

Steam is a compressible gas where pipe line mass flow capacity depends on steam pressure.
• ### Sizing Steam Pipes (lb/h)

Steam is a compressible gas where the capacity of a pipe line depends on the size of the pipe and the steam pressure.
• ### Steam & Condensate Equations

Steam consumption and condensate generation when heating liquid or gas flows
• ### Steam - Flow vs. kW Rating

Calculate steam flow rate vs. kW rating.
• ### Steam Consumption for some Typical Steam Heated Consumers

Steam consumption rates for typical steam heated consumers in industries like bakeries, breweries, paper factories etc.
• ### Steam Heating Air

Calculate steam heated air systems.
• ### Steam Heating Systems - Classifications

Steam systems carries heat through pipes from the boiler to consumers as heat exchangers, process equipment etc.
• ### Steam Heating Systems - Design

An introduction to the basic design of steam heating systems.
• ### Steam Pipes - Sizing

Sizing of steam pipe lines - major and minor loss in steam distribution systems.
• ### Steam Radiators and Convectors - Heating Capacities

Steam radiators and steam convectors - heating capacities and temperature coefficients.
• ### Steam Trap Selection Guide

Steam trap selection guide - Float & Thermostatic, Inverted Bucket, Bimetal Thermostatic, Impulse and Thermodynamic Disc steam traps.
• ### Submerged Coils - Heat Transfer Coefficients

Heat transfer coefficients for steam and hot water coils submerged in oil tanks.

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## Citation

• The Engineering ToolBox (2003). Steam Heating Processes - Load Calculating. [online] Available at: https://www.engineeringtoolbox.com/steam-heating-process-d_437.html [Accessed Day Month Year].

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2.19.10