FAQ

There are two important criteria to be met in order to supply dry steam to steam-using processes. One is  vapor generation by means of a well-designed steam generator, and the other is condensate removal—condensate is formed when steam condenses in the steam lines on its way to the processes— through correctly designed steam pipes.

When selecting the operating pressure of a steam boiler,  the selected pressure value should not exceed that of the maximum pressure required by your processes; steam boilers can no longer generate dry steam if their operating pressure is 20% less than their design pressure.

Dry steam generation is directly related to the operating pressure, i.e., the latter should not drop. The steam generator’s capacity must be selected accordingly in plants with peak load demands. If the steam capacity is insufficient, a pressure drop will occur, and there will be water carryover in the piping system, regardless of the type of steam generator.

One might think that, at peak load demands, there will be no pressure drop in boilers because of steam accumulation; or that steam generators will experience pressure drop and generate wet steam, since there is no steam accumulation. That is not the case as we elaborate in response to the question: “At peak load demands, which is better: A Scotch boiler or a steam generator?”.

Due to radiation losses, the produced dry steam will condense along the steam distribution lines. In order to remove the condensate, the steam main should be installed with a slope of 1/70. Furthermore,  steam trap sets should be installed along the steam lines and at their end; also, separators should be placed in front of the processes.

In addition, solid particles—eroded from the pipes and entrained by the steam—can get into the processes. Removing welding burrs, especially for newly installed plants, may take weeks, or sometimes months. Therefore, a strainer with a 100 mesh screen must be installed at the inlet of all steam-using processes and said strainer must be periodically cleaned.

For more information, please call (+90) 212 595 16 56 or e-mail us at teknik@jenesis.com.tr.

On the market, systems with relatively low capacity and capable of producing steam very quickly compared to steam boilers are known as steam generators. In fact, steam generators may be thought of as small versions of water-tube boilers used at high pressures and high capacities. For a steam-generating system to be referred to as steam generator, it must be of water-tube design; systems of fire-tube design with a water tank are called Scotch boilers.

While steam boilers generate steam within 30–90 minutes, steam generators generate steam within 3–5 minutes at the desired pressure. Thus, steam generators allow significant reduction in costs upon first operation.

Steam generators have approximately 1/10 of the water volume in steam boilers. In addition, water is not stored within a vessel but passes through the tubes. As a result, steam generators have zero risk of explosion. Actually, they can be legally installed near residential areas.

Steam generators can generate steam as and when needed. Hence, very good automation and synchronization are required between the feedwater and combustion systems. Otherwise, wet or superheated steam can be generated.

Since water is not stored within the body in steam generators, surface or bottom blowdown is not required. In contrast to steam boilers, this is a huge advantage in terms of reducing losses.

Generally, steam generators are produced for steam capacities between 100 and 4,000 kg/h.

However, Jenesis, thanks to its HUB System, can generate steam at unlimited capacity.

As a result of the studies carried out by Jenesis’ R&D team over the last 10 years, by overcoming the limitations of conventional generators, Jenesis started to produce steam generators with enhanced features, high efficiency, and low operating costs.

For more information, please call (+90) 212 595 16 56 or e-mail us at teknik@jenesis.com.tr.

Steam generators only contain 1/10 of the water volume in fire-tube boilers. Moreover, in steam generators, this water volume is not stored outside of the heat transfer pipes. Rather, water flows through them. Thus, steam generators have no explosion risk.

Recently, given the importance attributed to business continuity, occupational safety and health has become more valued. The effects of an exploding boiler are multiple; such an event will have physical as well as psychological impacts on an individual’s life.

Steam generators are preferable for several reasons such as the relatively lower installation costs of a separate boiler room, the effective use of the site, the occupational safety and health aspects, as well as the low operating costs.

For more information, please call (+90) 212 595 16 56 or e-mail us at teknik@jenesis.com.tr.

In order to remove corrosive gases such as oxygen (O2) and carbon dioxide (CO2) in the feedwater, the latter needs to be heated.

While CO2 is completely removed from the water at 65 °C and above, O2 is completely eliminated at 102 °C. Since, in some facilities, the temperature of the condensate tank automatically rises to 80–90 °C, no deaerator is required; to prevent corrosion, the remaining amount of O2 can be neutralized—at relatively low initial and operating costs—by means of oxygen-scavenging chemicals.

In any case, feedwater temperatures vary between 85 and 105 °C. When pumping feedwater into the steam generators at high pressures, vacuum is formed at the suction side of the pump. Due to high feedwater temperature under vacuum conditions, cavitation occurs as a result of water evaporation and volumetric expansion.

In attempts to prevent cavitation, aiming to reduce the temperature of the condensate tank by draining it and replacing the hot condensate with cold one is not the right approach—as it implies energy loss, additional water treatment costs since high-quality water has been disposed of, as well as corrosion.

Therefore, by installing condensate tanks or deaerators at a certain elevation, the feedwater pump should operate with a high NPSH, i.e., the local static pressure at the pump inlet should be high. For instance, a deaerator operating at 105 °C is required to be at least at 5m above the pump.

If the condensate tank or deaerator cannot be placed higher, a relatively cheap circulation pump can be installed between the feedwater tank and the pump, so as to prolong the feedwater pump’s life.

Circulation pumps move the high-temperature feedwater from the condensate tank or deaerator to the main feedwater pump and prevent cavitation in the latter by creating a positive pressure on their suction side.

Also, there are models of feedwater pumps used in steam generators that are equipped with a cooling jacket. To prevent the hot feedwater from damaging the internal structure of the pump, cold water is circulated through the jacket within which the pump is enclosed, thereby protecting the pump.

For more information, please call (+90) 212 595 16 56 or e-mail us at teknik@jenesis.com.tr.

There are two crucial factors which affect steam generation efficiency: combustion efficiency and heat transfer efficiency.

Burner selection is crucial for achieving high combustion efficiency.

With today’s technology, choosing a proportional control burner over a single-stage or two-stage one is not enough. Among proportional control burner, there are mechanically as well as electronically controlled models; among these models there are the low-NOx types—which are environmentally friendly. Also, combustion efficiency can be specified by means of Class I, II, III classifications.

In addition, for high-efficiency combustion, your burner should not be selected based on the steam capacity limit.

The combustion settings of the burners are adjusted according to the instantaneous gas pressure and the air conditions. However, since these values change in time, the combustion settings are also affected. Hence, in order to ensure that the combustion parameters are constant, the use of oxygen trim systems—which can continuously adjust the combustion parameters, depending on the amount of oxygen in the flue stack—is recommended.

On the other hand, it is crucial to transfer the energy obtained from the combustion to the water through the pipes. While looking at the steam capacity of steam generators (in kg/h), it is also necessary to consider the heat transfer area (in m2). This is because the energy from the combustion can be lost through the flue stack before it can be transferred to the water.

In an ideal steam generator, the design is made under the assumption that 1000 kg/h of steam can be generated for every 40 m2 of surface area. In steam generators will reduced heat transfer area, the efficiency decreases and wet steam is produced.

For instance, a steam generator with a 5,000 kg/h capacity should not have a heat transfer area less than 5 x 40 = 200 m2.

Another important factor is the number of passes of the steam generator’s tubes; an ideal steam generator should have 3 passes. The efficiency is lower in single-pass or two-pass steam generators. In that case, huge losses are incurred by the increase in operating costs.

Also, using proportional control for the steam generator’s feedwater system and reducing burner peak loads contribute to the generation of higher-quality steam.

Furthermore, choosing a frequency-controlled feedwater pump allows electricity savings.

In steam generators, the flue gas temperature can be in the range of 200–350 °C. Hence, it is important to recover the energy contained in the flue gas.

Economizers, which allow us to transfer the flue gas energy to the water; and recuperators, which enable us to transfer the flue gas energy to air, should be indispensable parts of steam generators.

It is worth noting that, upon recovering the heat in the flue gas, every 20 °C decrease in the flue gas temperature corresponds to an increase in the generator’s efficiency by approximately 1%.

For instance, in a steam generator, if the flue gas temperature is decreased from 240 °C  to 120 °C, then  120/20 = 6% of energy savings can be achieved.

Although there are no losses due to blowdown in steam generators, if you own a fire-tube steam generator, the energy from surface as well as bottom blowdown can be recovered.

By means of a flash steam recovery system installed at the surface blowdown system outlet, the blowdown heat is extracted and the cold water is then drained.

In facilities using deaerators, some steam is discharged to the air with the corrosive gases through the vent. The energy of said steam, which was released without any control, can be recovered.

Using heat exchangers made of special materials with high corrosion resistance, energy savings can be made by reclaiming the heat of the discharged steam. 

For more information, please call (+90) 212 595 16 56 or e-mail us at teknik@jenesis.com.tr.

To add to our reply to the question “How can I generate steam more efficiently”, here are 4 important ways to reduce steam production costs:

  • Hot water production using JetPack

In most facilities, in order to meet the energy needs at peak load demands, accumulation tanks or storage water heaters are used. In such systems where a large volume of water is stored, radiation losses continuously occur within 24 hours.

The tubed heat exchanger in a storage water heater has a lower efficiency compared to a plate heat exchanger, and presents difficulties for maintenance and repair operations.

Due to risk of Legionnaire’s disease, the hot water should be stored at a temperature of at least 65 °C, which increases the operating costs. In lieu of the aforementioned systems, the use of the JetPack hot water production system—which does not require accumulation tanks and can meet hot water needs at peak demands—enables energy savings.

  • Controlling the effectiveness of insulation

Since they are located underneath the outer jackets, the effectiveness of insulation layers is unknown.

Hence, it is required to measure the effectiveness of insulation layers by means of thermal cameras and make the necessary improvements. Insulating non-insulated pipes and using valve jackets yield significant energy savings. Also, there has been a significant interest in insulation coatings for facilities where using standard insulation materials is not possible.

  • Installing flash steam recovery system

The flash steam from the condensate return lines does not have to be discharged into the atmosphere through the condensate tank’s vent.

Instead, flash steam and condensate are separated by means of a flash steam recovery system—placed in front of the condensate tank—condensate is then sent to the condensate tank without its energy intact and the energy of the flash steam can be used to produce hot water or hot air. 

  • Installing a steam trap monitoring system

When steam traps do not operate properly, they can remain closed, thereby prolonging the production time in processes; or stay open all the time, causing live steam to escape.

Even if steam traps of the highest quality are selected, they may not work properly within a short time period due to installation errors, water hammer from the pipes, or impurities.

The cost of the escaped steam or the production loss is quite high compared to the steam traps’ cost.

Hence, having an online system which can monitor the state of the steam traps, i.e., whether the steam traps are operating properly is essential in tracking and minimizing losses.

For more information, please call (+90) 212 595 16 56 or e-mail us at teknik@jenesis.com.tr.

The SHS series and HUB System steam generators produced by Jenesis Steam Systems are of water-tube design and contain 1/10 of the water volume in fire-tube designs.

In addition, the water is not statically stored outside the pipes but flows through them.

Also, per our design standards, the maximum pressure the pipes can withstand is around 250 barg at the steam’s temperatures. Not only can these specially designed pipes withstand high pressures, but they are also designed with increased corrosion resistance.

Per our standard, the design pressures of Jenesis steam generators are between 3 and 10 barg. Upon request, the generators can be produced at higher design pressures.

Owing to these features, the Jenesis steam generators have zero risk of explosion.

Thanks to the HUB system, steam boiler houses can be installed without any capacity limit with the modules connected cascaded. In the HUB system, 30 t/h boiler rooms can be installed by connecting 10 modules cascade of 3 t/h. Depending on the requirements, owing to its automation system, the HUB system can operate as many modules as necessary while keeping them at their highest efficiency.

Furthermore, it is noted that, by recording their individual running times, the modules may be operated such that they will have had equal running time within a certain time period.

Another advantage of such a flexible system offers to factories is that, if, for whatever reason, there is a change in production capacity, the  modules are operated at their highest efficiency and according to the demands—only a number of modules are operated to meet the desired steam capacity—thereby reducing the operating costs.

For more information, please call (+90) 212 595 16 56 or e-mail us at teknik@jenesis.com.tr.

One of the most important parameters which indicate the efficiency of steam generators is the flue gas temperature; the higher the temperature of the combustion gases, the lower the efficiency of the steam generator.

Here are four reasons why the flue gas temperature may increase:

  • First, the design of the steam generator is essential. In single-pass or two-pass designs, high flue gas temperature is expected. Therefore, ideally, we recommend the use of three-pass steam generators. Regardless of the number of passes, the generator must have sufficient heat transfer area.

A steam generator is designed assuming that 1,000 kg/h of steam is generated for every 40 m2

area. For instance, a steam generator with a 5 t/h capacity should not have less than  5 x 40 = 200 m2 heat transfer area.

If there is less heat transfer area, the energy of the exhaust gases cannot be adequately transferred to the water and is wasted when the gases are discharged at higher temperatures. Thus, your efficiency decreases and your fuel expenses increase.

  • The combustion efficiency of the burners is one of the factors that directly affect the flue gas temperature. Hence, it is advantageous to continuously monitor the burner’s performance.

Sometimes, in order to rapidly respond to peak steam demands, the combustion may occur with excess fuel and less oxygen in the mixture, i.e., a fast but inefficient combustion may take place in response to the demands.

The pros and cons of this method should be evaluated so as to come up with more effective solutions.

On the other hand, since the seasonal adjustments of the burner settings depend on the gas pressure and atmospheric conditions at the time of the adjustments, and that the air conditions or gas pressure may change even within hours, the combustion quality will decline; the flue gas temperature increases while the efficiency decreases.

Thus, the ideal solution is to adjust the combustion settings instantly by monitoring the amount of oxygen in the flue stack using oxygen trim systems.

  • Another crucial point is the efficiency of the heat transfer from the combustion gases to the water. Given that scale on the surfaces affects heat transfer, the energy of the flue gas is wasted; the flue gas is discharged to the atmosphere without its energy properly extracted. The absence of scale depends on the quality of the feedwater and its continuous supply. Moreover, failure to keep conductivity levels under control will result in scale formation in steam generators. It is important that the feedwater has zero hardness and, if possible, low conductivity.

If a fire-tube steam generator is used, its blowdowns should be carried out by means of automatic blowdown systems.

  • If all the optimal conditions are met, i.e., if the combustion quality is high with a trim system; the water is of high quality using reverse osmosis systems; and there is sufficient heat transfer area, the energy of the hot flue gas ought to be extracted by means of an economizer. It is possible to increase the efficiency by 5 to 8% using condensing or non-condensing economizers.

For more information, please call (+90) 212 595 16 56 or e-mail us at teknik@jenesis.com.tr.

In plants with no deaerators, the temperature of the condensate tank should be between 80 and 90 °C. At temperatures at or below 80 °C, there is a large amount of dissolved oxygen (O2) in the water. The O2, entering the system with the water, leads to corrosion of the steam generator’s internals, thereby reducing the system’s life. This is a huge risk and means increased costs.

While oxygen-scavenging chemicals can be used to neutralize the O2 in the condensate tank, the amount of chemicals to be dosed increases since the O2 amount increases parabolically at temperatures below  80 °C. Adding an excessive amount of chemicals to the water incurs higher costs and causes the water to be saturated within a short time period. For the chemicals to be effective, the saturated water ought to be drained, i.e., the water quantity for the blowdown is increased, and replaced with fresh water. Operating costs will increase since the drained water is hot and has been treated. Therefore, temperatures below 80 °C are not reasonable.

Similarly, temperatures above 90 °C are undesirable due to potential cavitation in the feedwater pumps; radiation losses from the condensate tank will increase and the pump’s life will be shortened.

If your thermometer is not defective, the condensate tank temperature may increase due to 4 main reasons:

  • It is possible that, due to steam trap leaks, not only hot condensate and flash steam reach the condensate tank, but also live steam. Leaking steam traps can incur serious losses to processes, raise the temperature of the condensate tank, and damage the feedwater pumps.

Therefore, steam traps should be regularly monitored and controlled, and the leaks should be properly managed.

  • Another issue is that the operators open the steam traps’ bypass lines to reduce the running time of processes and solve the wet steam issue. Operators opting for this approach are unaware of the damage they cause, especially in case of incorrectly selected or defective steam traps. Thus, it is important to ensure that the operators have training, the adequate steam traps are selected, and the steam traps function properly.
  • Due to the failure of the feedwater control system, with only condensate flowing into the tank and water being manually supplied at certain intervals, the temperature of the condensate tank varies within a large range. Hence, it is essential to ensure that the water level controller is functioning properly.
  • Another crucial point is the condensate tank vent; it may not be properly sized or is closed.

Condensate tanks must be at atmospheric pressure. In case of closed condensate tank systems, i.e., pressurized tank systems, all the processes and steam traps must be designed accordingly. Since 99% of plants are easy to operate, they are designed with an open condensate system. For this reason, it is recommended that the flash steam, which comes with the hot condensate from the return lines, be separated by means of a flash steam recovery system placed before the condensate tank.

For plants without said system, the flash steam needs to be discharged to the atmosphere through the condensate tank vent. In that regard, the vent’s diameter must be chosen such that all the flash team does not accumulate in the tank but is totally discharged.

Otherwise, the temperature and pressure of the tank will increase.

For more information, please call (+90) 212 595 16 56 or e-mail us at teknik@jenesis.com.tr.

Water quality is essential in steam generation; it affects the proper operation, efficiency and even the life of the system.

As the water goes from a liquid to a gaseous state, i.e., during phase change, since the solid particles contained in the water cannot be carried over with the steam as it leaves the steam generator, the solid particles build up in the remaining water.

If there is water carryover in the system, said impurities are contained within the water droplets in the steam and may enter the processes. Solid particles carried along with the water may deposit on the heat transfer surfaces, causing a decrease in efficiency as well as steam trap malfunction.

We are talking about serious energy losses; even a 1 mm-thick scale—which might seem insignificant to the naked eye—may result in 8% decline in efficiency.

Due to the aforementioned reasons, water with zero hardness should be fed into all steam generators so as to prevent scale formation.

Solid particles that remain in the steam generators build up over time on the heat transfer surfaces, thereby reducing efficiency, causing corrosion, and inducing thermal stresses to the structure.

As a result, the amount of solid particles—which increase the electric conductivity of the water—needs to be kept under the allowable limits by means of automatic blowdown systems.

However, since a significant amount of hot water is drained, that is, energy is wasted during the blowdown process, there should be a heat recovery system at the outlet of the blowdown system or the blowdown volume should be reduced.

One way to reduce the blowdown water quantity is via reverse osmosis (RO).

With the solid particles in the feedwater removed and the conductivity brought down to very low levels, the buildup of solid particles in the steam generator will significantly decrease and the blowdown quantity will be minimized. Hence, it is imperative that feedwater with zero hardness is fed to steam generators. Ideally, we recommend that the feedwater has zero hardness and low conductivity.

Another critical issue is the elimination of dissolved gases such as oxygen and carbon dioxide in the water. Given that these gases are highly corrosive, they must be removed before the water is fed to the steam generator. This can be achieved in two ways: using thermal (conventional) deaerators—heating the water using live steam, the dissolves gases and a certain vapor quantity are discharged into the atmosphere; or using oxygen-scavenging chemicals while maintaining the temperature of the condensate tank above 80 °C.

For more information, please call (+90) 212 595 16 56 or e-mail us at teknik@jenesis.com.tr.

Compared to fire-tube boilers, steam generators are in fact water-tube steam boilers with relatively low capacity. In both designs, burners of the same type and capacity may be used.

If they are designed correctly, high-quality, dry steam can be generated in both fire-tube and water-tube boilers. Steam can be generated using these boilers or similar systems, and can be used in all sectors. Regardless of the industry type, steam generators can generate high-quality steam at constant pressure.

Processes or industries may have different steam consumption habits. This may affect the capacity selection depending on the calculated peak load demands and running time. In any case, both fire-tube and water-tube steam generators can be used.

For more information, please call (+90) 212 595 16 56 or e-mail us at teknik@jenesis.com.tr.

When we reduce the operating pressure in the steam generator, 4 situations occur.

  • First, if among the steam generators, you use the ones of water-tube type, reducing the operating pressure does not affect the steam quality.

However, in fire-tube systems, if the operating pressure is 20% less than the boiler design pressure, wet steam generation increases due to relative changes in the water level.

In that case, issues including erosion, corrosion, water hammer, and efficiency drop arise.

In the whole plant, these issues may occur in an unforeseen or unpredictable manner.

  • When the steam pressure is decreased, the amount of energy required to generate steam, i.e., the amount of fuel required decreases. However, this decrease in fuel consumption may be less than the expected amount.

For example, if you want to operate a steam boiler with an operating pressure of 10 barg (hg = 2,781.7 kJ/kg) at 6 barg (hg = 2,763.5 kJ/kg)—since the highest demand in your process is at 6 barg, the amount of fuel required will decrease by only (2,781.7 – 2,763.5)/2781.7 = 0.0066, i.e., 0.66%.

  • Lowering the pressure will also lower the temperature; for instance, while the saturation temperature is 184 °C at 10 barg, it drops to 165 °C at 6 barg.

Hence, as the temperature of the steam going to the processes decreases, the efficiencies of the processes will also decrease.

Let us recall the heat transfer relation .

In this expression, if the temperature difference  is decreased, the amount of heat transfer at the rate of the temperature difference will also decrease since the surface area  and the heat transfer coefficient  remain constant.

In our previous example where the operating pressure is 6 barg instead of 10 barg, the temperature will decrease by (184 – 165)/184 = 0.1033, i.e., 10%.

This means that your process will run by approximately 10% longer and your production capacity is reduced by 10%.

  • Another crucial point to consider is that, if the steam and condensate lines have been designed for high pressure, your installation may not be able to carry the required steam capacity, upon reducing the operating pressure. This is because the pipe diameter should be enlarged when the pressure drops. Otherwise, steam whose speed has exceeded the allowable limits causes more erosion and water hammer. Also, due to high speed, the pressure drop increases and so do the losses in the plant.

Hence, we recommend the following: the operating pressure of steam generators should not be reduced; the steam generators should operate at the pressure they are designed for; the steam should be carried to the processes at high pressure, and the steam pressure should then be reduced by a pressure reducing station installed close to the processes.

For more information, please call (+90) 212 595 16 56 or e-mail us at teknik@jenesis.com.tr.

Corrosive gases such as oxygen (O2) and carbon dioxide (CO2) in the feedwater must be removed before the water is fed into the steam generator. This can be achieved in two ways. The first method consists of heating the condensate; CO2 will have been removed from the feedwater at a temperature of 65 °C and O2 at 102 °C. The second method is the use of chemicals to neutralize the corrosive gases.

The condensate temperature, except in a few sectors, due to a high condensate return ratio, may reach 70–90 °C. In that case, all the CO2 has been removed. It is then required to eliminate the O2 from the water and discharge it.

When thermal or conventional deaerators are used, the condensate temperature is raised to 105 °C by feeding live steam into the device. In order to prevent cavitation in the feedwater pumps, the deaerator should be located at least 5 m above the pump.

In this case, a boiler room with a height of at least 10 m is necessary. If the height happens to be insufficient, a compact (modern) deaerator can be used.

The compact deaerator, a system in which a deaerator dome is added to the existing condensate tank, operates at the condensate tank temperature. However, the 2 most important differences are constant pressure and homogeneous temperature distribution.

While the temperature may reach 105 °C in conventional deaerators, the condensate is kept at a constant temperature between 85 and 90 °C in compact deaerators.

In conventional deaerators, all the O2 is removed and discharged with a small quantity of steam. In contrast, in compact deaerators, the remaining amount of O2 in the condensate tank—whose temperature is between 80 and 90 °C—is eliminated by means of oxygen-scavenging chemicals.

For instance, for a facility with a  steam generator with a capacity of 5 t/h, comparing the initial investment and operating costs between the two options will help us decide.

  • The initial investment costs are high for conventional deaerators. The cost of a separate pressurized tank and a stainless steel deaerator dome will vary from company to company, but with all the associated equipment, will amount to around 15,000-20,000 €.

The operating costs may be divided into two: radiation losses from the walls and the costs of the vented steam.

Radiation losses due to a separate deaerator dome should also be added to the operating costs.

Consider a storage vessel of a deaerator with a 5 m³ capacity. Closing all its valves and assuming that, within 1h, the temperature will have dropped from 105 °C to 100 °C:

 in 1h, i.e., 25,000 kcal/h. The corresponding volume flow rate of natural gas is: .

If we take the natural gas price as 0.25 € and assume that the system is to be used 20 hours a day, 300 days a year:  is obtained.

The approximate cost of the energy losses from the deaerator’s walls on a yearly basis can be calculated using the above method.

The amount of steam escaping through the vent valve can be calculated in the subsequent manner. In general, the DN25 vent valve is used, it is fully manually operated, and is to be left partially open. The steam leaving the valve will move up by at most 50–100 cm and, depending on the air current, will flow left or right.

Thus, while some steam may be discharged, the separated O2 in it is also vented out.

Although a DN25 valve varies from manufacturer to manufacturer, we can take the average Kv value as 12. Also, assuming that about 1/3 of the valve is open,  the approximate Kv value may be taken as 4.

If you have more specific data for your plant, you can obtain more accurate values for your applications with the formulas given below.

We know that our conventional deaerator is operated at a pressure of at least 0.2 barg. In this case:

M = 12 x Kv x P1 √ 1 – 5.67 (0.42 – χ)²   ,           χ = (P1 – P2)/P1 bara

            It can be determined from the above relations that 46 kg/h of steam will be vented out.

Assuming that 1 t of steam costs 20 €, and that the generator operates 20 hours a day and 300 days a year, the cost amounts to 46/1,000 x 20 x 20 x 300 = 5,520 €/year.

In this scenario, the initial investment costs of the conventional deaerator is up to 20,000 €, with annual operation costs up to 10,000 €.

  • As a second alternative, estimates should be made for plants using compact deaerators or plants whose condensate tanks are already at a temperature between 80 and 90 °C.

If only a condensate tank is used, there is no initial investment cost. Since there will be no additional storage vessel, related radiation losses will not occur.

In plants using a compact deaerator, the initial investment costs are about 10,000 €. There will be no additional radiation losses since the deaerator is installed on top of the existing condensate tank.

Chemicals are required to neutralize the oxygen dissolved in the water. Assuming that our condensate tank is at 85 °C, to capture the remaining oxygen amount, based on our meetings with chemical companies, for steam generation of 5 t/h and 80% condensate return ratio, it was evaluated that we additionally need to dose chemicals at 0.23  €/h.

Assuming that the operations last 20 hours a day and 300 days a year, the costs associated with oxygen scavengers amount to 0.23 x 20 x 300 = 1,380 €/year.

Whether to use a deaerator for the plant can be decided based on the above calculations and approximations.

For more information, please call (+90) 212 595 16 56 or e-mail us at teknik@jenesis.com.tr.

When setting up a factory, determining the steam capacity is very difficult because of technical constraints and uncertain future conditions.

Specifically, the high costs associated with operating large boilers are challenging to facilities whose production capacities have decreased in the event of a pandemic.

In this article, we will examine the types of generators in steam systems, their responses to peak load demands, and steam storage.

When determining the steam requirements of processes, steam consumption upon first operation, the future thermal loads on the steam pipes and on the processes themselves must be taken into account.

If these additional loads are not included in the steam capacity requirement, it should be accepted from the beginning that the start up time will be longer.

Another crucial point to consider is that, instead of the hourly nominal capacities given in the manufacturers’ catalogs, instantaneous peak demands should be accounted for while considering the steam consumption time—according to the processes’ specifications.

Determination of peak steam demands:

It will be easier to understand the topic with an example. Suppose that, according to the manufacturer’s catalog, a process consumes 100 kg of steam per hour.

However, in practice, within a 1 h period, having consumed steam within 10 min, item acquisition/discharge, detergent/chemical dosage, rinsing, waiting, etc. may take place within the remaining 50 min.

Despite the steam capacity of 100 kg/h, in practice, to be able to provide 100 kg of steam within 10 min to the process, the process should be able to instanly draw 100 kg x 60 min /10 min = 600 kg/h and the steam generator capacity should be specified accordingly.

If every process is designed based on the catalog data, in practice, the heating time will increase, thereby increasing the process time and decreasing the daily production capacity.

With a simple approach, if the instant steam consumption of the process is 600 kg/h as in the previous example, if we apply the same procedure again, it would not be wise to invest in 10 steam generators with a capacity of 6,000 kg/h in a factory.

This is because the number of processes with coincident steam consumption time, i.e., 10 min, needs to be known beforehand.

Also, potential overlaps in the processes’s instant steam demands need to be examined.

While analyzing these scenarios, the process time, the duration of instant steam demands, and the effects of the process operators’ tasks on the overlap ought to be considered.

It is essential to select steam generators which can meet the variability in facilities where peak steam demands are high.

Peak demands may last a few minutes or 10–15 min depending on the processes’ characteristics.

Investing in a large boiler to meet peak demands that will last 10–15 minutes is highly costly; furthermore, the operating costs will increase due inefficiency—since the boiler is operated at capacities much lower than its actual steam capacity throughout its life.  

At this point, it is necessary to examine the features and behaviors at peak demands of Scotch boilers—which are the most preferred in the industry— and steam generators.

Behaviors of different boiler types at peak load demands:

Scotch boilers possess a reservoir in which steam is stored. Also, a large volume of water is stored within their body. In contrast, steam generators only contain 1/10 of said water volume and steam storage is almost non-existent.

For example, let’s assume that a Scotch boiler with a capacity of 5 t/h, operating at 6 barg, stores approximately 8 m³ of steam and 15 m³ of water—this varies depending on the brand and the design.

Under the same operating conditions, a true water-tube boiler, i.e., a steam generator, contains 0.3 m³ of steam and 1.5 m³ of water.

It is worth noting that, since the specific volume of steam is very low, steam volumes have little significance when expressed in terms of masses.

For instance, at 6 barg, the specific value of steam is 0.272  m³/kg; in other words, 1 kg of steam at 6 barg occupies a volume of  0.272 m3.

In this case, for the boiler with a 5 t/h capacity in our example, the amount of steam stored is (8 m³) / (0.272 m³/kg) = 29.4 kg.

A steam generator with a capacity of 5 t/h can store approximately 30 kg of steam for (30 kg / 5000 kg) x 3600 s = 21.6 s.

In other words, in the event of peak demands, the amount of steam stored in Scotch boilers will only suffice for 22 s.

As the peak steam demands will take longer than 22 s, this time, the burner must operate at full capacity and the 15 m³ of water in the Scotch boiler is to be heated and evaporated into steam.

This indicates that the pressure drop in a Scotch boiler at peak demands will continue for a long time period and will require a longer time to reach the operating pressure.

Regarding water-tube steam boilers (steam generators), there is less amount of steam stored at peak demands and, through the same calculation method, it is determined that the amount of steam stored is not sufficient even for 1 s at peak load demands.

Therefore, taking the numbers in our example as references, pressure drop will start 21 s earlier compared to that in Scotch boilers.

However, using the previous numbers as references, we can say that both Scotch boilers (fire-tube boilers) and water-tube boilers (steam generators) will experience pressure drop lasting longer than 22 s at peak load demands.

Given that water-tube boilers (steam generators) contain 1/10 of the water volume in Scotch boilers, compared to the latter, the operating pressure can be reached 10 times faster and within a short time period.

Steam accumulation methods:

Sometimes, in plants where the boilers do not have sufficient capacity or they cannot meet peak load demands, it may be desirable to have steam storage vessels.

For instance, in order to store 1 t of steam at 6 barg, a volume of 1,000 kg x 0.272 m³/kg = 272 m³ is required.

Such a large storage vessel will not only incur very high initial investment as well as operating costs, but also be problematic to accommodate.

When such needs arise, it is more reasonable to design systems referred to as wet steam accumulators which operate on the principle that an amount of the water stored in the vessels is turned to steam when there is pressure drop.

While relatively high-pressure steam is sent to the wet steam accumulator and routinely used, due to the pressure drop at peak load demands, additional, low-pressure steam (flash steam) is generated—due to the evaporation of the water in the vessel.

The larger the pressure difference and water volume in the wet steam accumulators, the more flash steam can be generated.

This method, specifically designed for a given process and often used in the EPS sector, may prove advantageous in other sectors.

Changes in steam quality at peak demands:

In short, it is not accurate to say that Scotch boilers have sufficient or more steam stored; however, it can be said that, at peak load demands, water-tube boilers (steam generators) have a shorter response time and can reach the desired pressure values within a short time period.

Since they have fast response time, operate at low pressure, and can quickly reach the desired operating pressure, water-tube boilers (steam generators) are more advantageous; especially considering that low-quality steam is produced due to pressure drop at peak demands, and that there is wet steam carryover from the Scotch boiler.

For steam generators to properly respond to sudden changes, they need to be equipped with a very good automation system and possess a large heat transfer area. Moreover, it must be ensured that all its equipment is connected and synchronized.

In conventional steam generators where these criteria are not met, wet steam is produced not only at peak load demands, but also under normal operating conditions.

Water-tube boilers with flexible capacities:

It can be understood from the previous explanations that determining the required steam capacity is crucial. Given that the purchase of a steam generator is a one-time investment, it is generally a huge one considering long-term operations.

When the operations do not go as planned, high operating costs are incurred due to low efficiency and high cost of the boiler; sometimes, the operating costs may even exceed the initial investment costs.

On the other hand, if the boiler capacity is insufficient, huge investments may be required for a huge-capacity boiler.

The modular steam generation system known as HUB System, which provides flexible steam production, has become more preferable.

The system consists of relatively smaller modules, which can be purchased according to the needs.

Depending on the requirements, owing to its automation system, the HUB system can operate as many modules as necessary while keeping them at their highest efficiency.

Furthermore, it is noted that, by recording their individual running times, the modules may be operated such that they will have had equal running time within a certain time period.

Another advantage of such a flexible system offers to factories is that, if, for whatever reason, there is a change in production capacity, the  modules are operated at their highest efficiency and according to the demands—only a number of modules are operated to meet the desired steam capacity—thereby reducing the operating costs.

For more information, please call (+90) 212 595 16 56 or e-mail us at teknik@jenesis.com.tr.