The use of steam in industry has a long history, starting from its application in locomotives and the Industrial Revolution, up to the present day. Steam has become an essential and crucial part of modern technology. Without steam, industries such as food, textiles, chemicals, medicine, energy, heating, and transportation would not be able to exist or function as they do today.

Steam is an energy carrier that can be easily controlled, produced efficiently and economically from a central boiler, and distributed to various points of use. Therefore, when steam is supplied to a factory, it is considered as distributing and utilizing energy evenly across all points in the factory. For many reasons, steam is one of the most widely used energy carriers for transporting thermal energy. Its application is popular across various industries for a wide range of tasks, from mechanical power generation to heating air and other heat-related processes.

AIR AND OTHER INCONDENSABLE GASES

Air is present within the steam supply pipes and equipment at start-up. Even if the system were filled with pure steam the last time it was used, the steam would condense at shutdown, and air would be drawn in by the resultant vacuum.

When steam enters the system it will force the air towards either the drain point, or to the point furthest from the steam inlet, known as the remote point. Therefore steam traps with sufficient air venting capacities should be fitted to these drain points, and automatic air vents should be fitted to all remote points.

However, if there is any turbulence the steam and air will mix and the air will be carried to the heat transfer surface. As the steam condenses, an insulating layer of air is left behind on the surface, acting as a barrier to heat transfer.

Credit Spirax Sarco

Layers of scale found on pipe walls may be either due to the formation of rust in older steam systems, or to a carbonate deposit in hard water areas. Other types of dirt which may be found in a steam supply line include welding slag and badly applied or excess jointing material, which may have been left in the system when the pipework was initially installed. These fragments will have the effect of increasing the rate of erosion in pipe bends and the small orifices of steam traps and valves. For this reason, it is good engineering practice to fit a pipeline strainer. This should be installed upstream of every steam trap, flowmeter, pressure reducing valve and control valve. When strainers are fitted in steam lines, they should be installed on their sides so that the accumulation of condensate and the problem of waterhammer can be avoided. This orientation will also expose the maximum strainer screen area to the flow. A layer of scale may also be present on the heat transfer surface, acting as an additional barrier to heat transfer. Layers of scale are often a result of either:Layers of scale found on pipe walls may be either due to the formation of rust in older steam systems, or to a carbonate deposit in hard water areas. Other types of dirt which may be found in a steam supply line include welding slag and badly applied or excess jointing material, which may have been left in the system when the pipework was initially installed. These fragments will have the effect of increasing the rate of erosion in pipe bends and the small orifices of steam traps and valves. For this reason, it is good engineering practice to fit a pipeline strainer. This should be installed upstream of every steam trap, flowmeter, pressure reducing valve and control valve. When strainers are fitted in steam lines, they should be installed on their sides so that the accumulation of condensate and the problem of water hammer can be avoided. This orientation will also expose the maximum strainer screen area to the flow. A layer of scale may also be present on the heat transfer surface, acting as an additional barrier to heat transfer. Layers of scale are often a result of either:

• Incorrect boiler operation, causing impurities to be carried over from the boiler in water droplets.
• Incorrect water treatment in the boiler house.
• The rate at which this layer builds up can be reduced by careful attention to the boiler operation and by the removal of any droplets of moistur

THE STEAM AND CONDENSATE LOOP

How is steam generated, distributed, controlled and used?

How is the condensate recycled?

A basic overview of a steam system.

This Module of The Steam and Condensate Loop is intended to give a brief, non-technical overview of the steam plant. It offers an overall explanation of how the different parts of the steam plant relate to each other – and represents useful reading for anyone who is unfamiliar with the topic, prior to progressing to the next Block, or, indeed, before undertaking any form of detailed study of steam theory or steam plant equipment.

The boiler

The boiler is the heart of the steam system. The typical modern packaged boiler is powered by a burner which sends heat into the boiler tubes.

The hot gases from the burner pass backwards and forwards up to 3 times through a series of tubes to gain the maximum transfer of heat through the tube surfaces to the surrounding boiler water. Once the water reaches saturation temperature (the temperature at which it will boil at that pressure) bubbles of steam are produced, which rise to the water surface and burst. The steam is released into the space above, ready to enter the steam system. The stop or crown valve isolates the boiler and its steam pressure from the process or plant. If steam is pressurized, it will occupy less space. Steam boilers are usually operated under pressure, so that more steam can be produced by a smaller boiler and transferred to the point of use using small bore pipework. When required, the steam pressure is reduced at the point of use. As long as the amount of steam being produced in the boiler is as great as that leaving the boiler, the boiler will remain pressurized. The burner will operate to maintain the correct pressure. This also maintains the correct steam temperature, because the pressure and temperature of saturated steam are directly related. The boiler has a number of fittings and controls to ensure that it operates safely, economically, efficiently and at a consistent pressure.

Methods for Estimating Steam Consumption

Methods for Calculating Steam Demand for Continuous and Batch Processes, Including Warm-Up, Heat Loss to the Environment, and Steam Loss in Pipes

The optimal design of a steam system depends on accurately calculating the steam consumption rate, which leads to determining the appropriate pipe sizes and auxiliary equipment such as control valves and steam traps. Steam demand for a plant can be determined through several methods:

1. Calculation

Analyze the amount of heat required to heat the product using heat transfer equations, which provide an estimate of steam consumption. Although heat transfer is not an exact science and may involve many unknown variables, experimental data or similar applications can be used for estimation. The results are often accurate enough for most applications.

Basic Equation:

Q=m⋅cp⋅ΔT

Where:

• Q = Heat required (kJ)
• m = Mass of the product (kg)
• cp= Specific heat of the product (kJ/kg·°C)
• ΔT = Temperature increase (°C)

Then, calculate the required steam mass using the latent heat of vaporization: m steam= Q / hfg​ ​

Where:

• m steam = Required steam mass (kg)
• hfg​ = Latent heat of vaporization (kJ/kg)

Considering Losses:

• Heat loss to the environment: Calculated based on heat transfer coefficients and surface area.
• Steam loss in pipes: Accounts for leaks and condensation in pipes.

2. Measurement

Steam consumption can be determined by direct measurement using flow meters, which provide accurate data on steam usage in the plant. However, for plants still in the design phase or not yet operational, this method is not feasible.

3. Reading from Equipment Name Plates

The heat consumption rate (or design rating) is often indicated on the nameplate of steam-using equipment. Manufacturers typically specify the expected heat load in kilowatts (kW) or other units, but the required steam mass flow rate (kg/h) depends on the operating steam pressure.

Considerations:

• Values on nameplates are ideal values obtained under controlled test conditions.
• Actual heat and steam consumption may differ due to factors such as environmental conditions, maintenance, and actual usage.

4. Comprehensive System Calculation

When designing a steam system, the following factors must be considered:

• Warm-Up: Heat required to bring the system or equipment to operating temperature.
• Heat loss to the environment: Calculated based on heat transfer coefficients and surface area.
• Steam loss in pipes: Accounts for leaks and condensation.

Overall Formula:

m total=m total​=m process​+m warm−up​+m loss​

Where:

• m total​ = Total steam demand (kg/h)
• m process​ = Steam demand for the main process (kg/h)
• m warm−up​ = Steam demand for warm-up (kg/h)
• m loss​ = Steam loss to the environment and in pipes (kg/h)

Conclusion

Calculating steam demand requires considering various factors, including the main process, warm-up, and losses. Using calculation methods, measurements, and equipment manufacturer data helps achieve accurate estimates for designing an efficient steam system.

Heat Recovery System

Why Should We Recover Heat from Condensate?

In 1 ton of condensate at 95°C, there is residual thermal energy of 292,600 kJ, which is equivalent to approximately 14 liters of Fuel Oil C. With Fuel Oil C priced at 16 baht per liter, the value of 1 ton of condensate is approximately 224 baht / ton.

If condensate is discharged at a rate of 1 ton per hour, it will result in a significant financial loss of 537,600 baht per year (Note: Operating 8 hours/day, 300 days/year).

If you are interested in reusing condensate to save costs, we are happy to offer a free on-site assessment to provide an investment proposal for a condensate recovery system. We are confident that the payback period for the investment will not exceed 6 months.

If you are interested in a proper condensate recovery system, please contact us at:

• Phone: 085-679-5642
• Email: nakhon@fluidline.net
• Website: https://www.fluidline.net

We sincerely hope to collaborate with you for mutual success at the earliest opportunity.