DE102005006137B4 - Method for energy input by heating steam by means of a device for heat transfer - Google Patents

Abstract

method for introducing energy to a product via a heat transfer device by condensation of steam, characterized in that the occurring Vapor pressure on the heating steam side of the device independent of the Heizdampftemperatur by additional supply of inert gas the Heizdampfseite kept larger is considered the back pressure of the condensate drainage system.

Description

object The invention is a method for energy input by heating steam by means of a device for heat transfer, and the device, which by the targeted use of inert gas improved controllability on the steam side of the device has the heating power.

In Chemical and industrial plants use different heating systems Input of energy, for example in distillations of products, for use. One differentiates systems, which operated with steam of those using liquid heat transfer media. Which Systems find use depends among other things, which quantities of energy have to be transferred.

In a device for heat transfer, only the available contact surface A is essentially effective for the heat transfer. If a particularly large amount of energy to be entered, this is done by heating systems that are operated with steam, for example, the enthalpy of vaporization with Δh _V = 2200 kJ / kg for water / steam at 1 bar _abs , is considerably greater than the specific heat capacity c _p = 4.18 kJ / kgK of water. That is, the condensation of the water vapor on the contact surface A provides many times more energy for the transfer than the contact with liquid, hot water on the same surface A. This fact is derived from equations (1) and (2) ).

Δh_V Verdampfungsenthalpie [kJ/kg]
bedeuten.Equation (1) applies to evaporation / condensation with Δh _V = 2200 kJ / kg for water / steam at 1 bar _abs Q = m · Δh V (1) in which
Q thermal output [W],
m mass flow

Δh _V enthalpy of vaporization [kJ / kg]
mean.

c_p spezifische Wärmekapazität bei konstantem Druck [kJ/kgK],
ΔT Temperaturdifferenz (T₁ – T₂) [K],
T₁ Temperatur des Heizdampfs bei der Kondensation [K],
T₂ Temperatur Produkt [K]
bedeuten.Equation (2) applies to heating / cooling with c _p = 4.18 kJ / kgK for water Q = m · c p · ΔT (2) in which
Q thermal output [W],
m mass flow

c _p specific heat capacity at constant pressure [kJ / kgK],
ΔT temperature difference (T ₁ - T ₂ ) [K],
T ₁ temperature of the heating steam at the condensation [K],
T ₂ temperature product [K]
mean.

A verfügbare Wärmeübertragungsfläche [m²],
ΔT Temperaturdifferenz (T₁ – T₂) [K],
T₁ Temperatur des Heizdampfs bei der Kondensation [K],
T₂ Temperatur Produkt [K]
bedeuten.The condensation of water vapor in suitable heat exchangers is widely used for the transfer of large amounts of heat in the industry and the heat output thereby transferred can be easily described by equation (3). Q = k · A · ΔT (3) in which
Q thermal output [W],
k heat transfer coefficient

A available heat transfer area [m ² ],
ΔT temperature difference (T ₁ - T ₂ ) [K],
T ₁ temperature of the heating steam at the condensation [K],
T ₂ temperature product [K]
mean.

Out Equation (3) results in two principal possibilities, the regulation of the transmitted Amount of energy.

at the condensate side control is the condensate drain over a Stand control in free flow or by pump as forced delivery regulated, whereby the condensate level in the device for heat transfer changed becomes. This regulation varies the condensation of the heating steam available area A from equation (3).

In the steam-side control, the steam supply is controlled by a suitable control element, whereby the pressure of the heating steam is changed in the device for heat transfer and thus the condensation temperature. With this method, the temperature T ₁ and thus the temperature difference .DELTA.T from equation (3) between heating steam and product is varied.

at the operation of steam-heated heat transfer devices also show diverse Disadvantages regarding the condensate level and steam control. Especially with highly reactive Products are also product-specific safety aspects to be observed.

The Condensate-side regulation is system-related relatively sluggish, since only by a level change the condensate level a control effect is achieved. level changes are because of the finite size of piping and regulatory organs only relatively slowly perform. Especially in distillation columns is a slow heat output control usually not tolerate. At the initiation of under high pressure standing condensate in the low pressure condensate network may be undesirable Steam hits come. By the design of the device for heat transfer and the interpretation of the condensate control valve, this can be suppressed, but too high Requirements on the planner and thereby increased investment costs. moreover reduce steam shocks the life of a plant and increase the maintenance costs. Especially with lying devices for heat transfer can impermissible thermal stresses occur because the vapor space at high temperatures isothermal and the condensate area at the lower temperature of the condensate is operated. Another disadvantage is that in the border area Steam / condensate reinforced corrosion damage may occur.

Due to the often required, large control range when heating with heating steam or variable operating conditions arise temporarily or constantly lower condensation pressures than the back pressure in the condensate system and condensate drainage is disturbed. This occurs particularly often when entering systems, systems that temporarily have a better heat transfer due to new or cleaned devices for heat transfer, or when operating systems in part-load operation far below the apparatus design. The resulting condensate accumulation leads to an increase in the condensation pressure until a sufficient differential pressure has built up again to the condensate system. Depending on the overall control strategy either the condensate level is maintained and the heating takes place at a high temperature level or the system is in vibrations with pulsating condensate level and consequently a turbulent energy input. If the condensation pressure below a bar _abs, for example, at heating steam temperatures below 100 ° C, the condensate can no longer flow freely. A safe condensate disposal can only be done here by the use of a suitable pump for forced delivery, which also leads to additional investment and operating costs.

Because of the manifold problems of condensate level control for heating power control in the industry mainly the heating steam control is used. But also in the heating steam control problems arise, which can be derived from the thermodynamically justified dependence of the vapor pressure on the temperature, as shown in Table 1 by way of example for water as the heating medium. Here, the demand for a wide range of heating power control of the strong dependence of the vapor pressure of the steam temperature opposite or contrary, since the vapor pressure decreases sharply with falling temperatures.

Table 1:

to optimal heating of a plant should the steam temperature in one preferably wide ranges are varied. This variation bandwidth becomes in the method according to the state The technique is limited by that depending on the local Conditions of the condensate drainage system below a certain Vapor pressure no orderly condensate removal is possible. It depends from the local Conditions below a certain vapor pressure to a condensate jam with the ones already listed Problems. The heating power control by heating steam control is thus problematic only if the vapor pressure is less than the Counterpressure of the condensate system is.

Safety-related problems often arise in addition to the technical-economic problems of the conventional control strategies already described, since, for safety or production reasons, the contact of water with product must be prevented or at least limited in the case of a leak in the device for heat transfer in some industries , In the case of a leak in a condensate-level device, the amount of water available for interaction with the product is substantially greater than in an ideal condensate drainage device where there is almost no condensate on the heating steam side of the device. This is illustrated in Table 2, which shows the increase in the available volume of water in the same volume, according to the density, [kg / m ³ ] depending on the heating medium used, in this case water, and its temperature in the heating steam. In order to comply with these safety aspects, special and thus investment-intensive constructions of the device for heat transfer, such as safety heat exchangers with double tubes are used.

Table 2:

at strongly throttled heating capacity builds up in the evaporator, the constructive for normal load was designed, a condensate level with the disadvantages already outlined on. If that's not allowed is, for example, a distillation column uneconomic, at higher returns and thus higher Energy use are operated, as it is in the current load condition would be required.

The present invention is therefore based on the object to provide a method for energy input by heating steam by means of a controllable device for heat transfer available. In this case, an orderly condensate removal by steam-side control should always be guaranteed, and the condensate level should be kept as low as possible on the apparatus-related minimum level, even if the vapor pressure is less than the back pressure of the condensate system.

Surprised was found to accomplish this object by the method according to the invention according to claim 1 solved becomes. The subject of this invention is a method for entry from energy to a product over a device for heat transfer by condensation of steam, characterized in that the occurring Vapor pressure on the heating steam side of the device independent of the heating steam temperature by additional supply of inert gas higher on the heating steam side is held as the back pressure of the condensate drainage system. Is preferred the vapor pressure on the heating steam side is 0.1 to 1.0 bar higher than the back pressure of the condensate drainage system. Preference is given to steam Steam for used this method.

at the method according to the invention Preferably, a targeted addition of inert gases to the vapor. This is the heat transfer and thus the heat transfer coefficient k is influenced by equation (3). The gas dosage thus affects to the third parameter of equation (3). Thus, a improved controllability of heating power achieved because the gas admixing almost a shift of the working range of the heat exchanger to higher Steam temperatures leads and thus to higher ones To press. The control of the heating power can thus continue through the Heizdampfsteuerung respectively.

The fed gas is referred to as inert gas, as it possible low interactions, such as solubility or reactivity, with has heating steam or condensate. Furthermore, in case a leakage also a largely inert behavior to the heated Product and heating steam given.

For the use according to the invention is the introduced inert gas selected from the groups containing Helium, neon, argon, krypton, xenon, radon, compressed air and nitrogen or mixtures thereof. Preferably, nitrogen is used, as this Gas almost no interactions with water and most, too has heated products. Furthermore, it is good in the industry available and relatively inexpensive.

The according to the invention, controlled Introduction of the inert gas can for example via a pressure reducer or via a Pressure control done. The pressure control can, for example, as Fertiggerät or be constructed as a pressure control line of individual components. The appropriate selection depends on the quality of the inert gas supply and the requirements of the operator. When using a pressure reducer the pressure in the inert gas network may fluctuate only slightly. With fluctuating Inert gas pressure, the desire for good operability or at required visualization / remote control of Inertgasdosierung is the pressure control preferred to use.

The Installation of a pressure reducer or pressure regulator for the fed Inert gas serves to in the vapor space of the device for heat transfer to produce a minimum pressure, whereby the condensate level on the apparatus-related minimum level is brought, as well as the continuous Condensate drainage is guaranteed. This is a precise, trouble-free Heizdampfregelung also possible in those cases where the current State of the art, the Heizdampfregelung fails. Like for example at oversized Heat exchanger surfaces or at times better heat transfer for new or cleaned heat exchangers and also at part-load operation far below the apparatus design as well during operation of the system, where the vapor pressure is less than the back pressure of the condensate system is. By the method according to the invention the emergence of a condensate level on an apparatus-related brought the lowest level, so that disadvantages such as corrosion damage, higher maintenance costs and reduced life can be avoided. In addition, there is a important safety advantage because of the introduction of inert gas, the condensate level is minimized and thus at a Leak a much smaller amount of condensate with the product in Contact is coming.

For a further preferred embodiment can on the inert gas, as well as the steam side different security measures introduced become. If the maximum inert gas pressure upstream of the metering device is higher than the permissible Pressure of the device for heat transfer is, the device may preferably with at least one sufficient sized safety valve in addition be secured. To avoid vapor backflow into the inert gas network, for example at inert gas failure or at higher Steam as inert gas pressure, can preferably suitable Rückströmsicherungen to be built in. For frost-prone Installation of the inert gas metering can preferably short lines between the dosing and the point of introduction of the inert gas in the steam line or the heat transfer device are installed. Particularly preferred are these lines, the metering and the backflow protection equipped with an anti-freeze heating system.

A device for heat transfer is characterized in that in addition to the steam through a feed line, the inert gas is fed into the vapor space. The feeding of the inert gas takes place for example via the supplying steam line or via a connection directly into the steam space of the device for heat transfer. Such a device for heat transfer is exemplified in 1 shown. The device contains a steam supply line ( 1 ), a steam condensate discharge ( 2 ), a product supply line ( 3 ), a derivative for heated / vaporized product ( 4 ), an inert gas supply ( 5 ), an apparatus-related minimum condensate level ( 6 ), a control device for vapor pressure ( 7 ), a control organ for inert gas ( 8th ), a control device for the steam condensate discharge ( 9 ), a contact surface ( 10 ), a heating steam space ( 11 ) and a supply line for inert gas in the Heizdampfraum ( 12 ).

The heat transfer device is characterized by being selected from the group consisting of shell and tube heat exchangers, plate heat exchangers, spiral heat exchangers and block heat exchangers. A preferred form is shown schematically in FIG 1 shown.

The heat exchangers have significant advantages, because they can be through a simple and inexpensive retrofitting with an inert gas supply even with existing systems getting produced. Also may be at the extra cost Dissipation of the condensate can be dispensed with by forced delivery. By the conversion have to No investment-intensive, specially designed heat exchangers be used, since the formation of steam blows through the invention is excluded.

Examples

Example 1 (not according to the invention):

This example refers to 1 with the difference that in the heat exchanger used no inert gas feed was present. For a Silandestillation a standard tube bundle heat exchanger was used which no inert gas feed line ( 5 ), no control element for inert gas ( 8th ) and no supply line for inert gas in the Heizdampfraum ( 12 ).

For the energy input condensation of the heating steam was sufficient at a temperature T2 of about 100 ° C. In heating steam room ( 11 ) resulted in a pressure P of about 1 bar absolute, but the back pressure P in the downstream Dampfkondensatableitung ( 2 ) was due to the system greater than the pressure P in Heizdampfraum ( 11 ). The steam condensate could be removed by the Dampfkondensatableitung ( 2 ) not free from the heating steam space ( 11 ) and thus there was a safety-critical backflow of the condensate level ( 6 ) in the heating steam space ( 11 ). This was problematic in terms of safety because there was extreme product incompatibility with the heating steam.

Example 2 (not according to the invention):

This example refers to 1 with the difference that in the heat exchanger used no inert gas feed was present. For a Silandestillation a standard tube bundle heat exchanger was used which no inert gas feed line ( 5 ), no control element for inert gas ( 8th ) and no supply line for inert gas in the Heizdampfraum ( 12 ).

Due to the production-related underload, the return flow to the column was reduced by 25% (which also corresponds approximately to an energy saving of 25%). For the energy input was now due to the reduced return flow, the resulting reduced column pressure loss and the lower product temperature condensation of the heating steam at a temperature T2 of only about 100 ° C. In heating steam room ( 11 ) resulted in a pressure P of about 1 bar absolute, but the back pressure P in the downstream Dampfkondensatableitung ( 2 ) was due to the system greater than the pressure P in Heizdampfraum ( 11 ). The steam condensate could be removed by the Dampfkondensatableitung ( 2 ) not free from the heating steam space ( 11 ) and thus there was a safety problematic backwater of the condensate level ( 6 ) in the heating steam space ( 11 ), because here too there was an extreme product incompatibility with the heating steam. For safety reasons, the return flow was then raised back to the original, energetically unfavorable value.

It an energy consumption of about 8 t / h heating steam was measured.

Example 3:

The same shell and tube heat exchanger was used for a silane distillation as for Example 1, with the difference that an inert gas feed line ( 5 ), a control organ for inert gas ( 8th ) and a supply line for inert gas in the Heizdampfraum ( 12 ) were retrofitted, and thus the 1 corresponded.

There was additionally a pressure-controlled ( 8th ) Supply of the inert gas ( 12 ) Nitrogen into the heating steam space ( 11 ), so that the heating steam at a temperature T2 of 110 to 120 ° C and a pressure P of 1.5 to 2 bar absolute in Heizdampfraum ( 11 ) condensed. The pressure P in the heating steam space ( 11 ) was thus greater than the back pressure P in the downstream Dampfkondensatableitung ( 2 ). The total pressure P in the heating steam space ( 11 ) was now high enough to allow the condensate into the existing steam condensate drain ( 2 ) could drain without a safety-critical condensate level ( 6 ).

Example 4:

The same shell-and-tube heat exchanger was used for a silane distillation as for Example 2, with the difference that an inert gas feed line ( 5 ), a control organ for inert gas ( 8th ) and a supply line for inert gas in the Heizdampfraum ( 12 ) were retrofitted, and thus the 1 corresponded.

There was additionally a pressure-controlled ( 8th ) Supply of the inert gas ( 12 ) Nitrogen into the heating steam space ( 11 ), so that the heating steam even at about 25% reduced return at a temperature T2 of 110 to 120 ° C and a pressure of 1.5 to 2 bar absolute in Heizdampfraum ( 11 ) condensed. The pressure P in the heating steam space ( 11 ) was thus greater than the back pressure P in the downstream Dampfkondensatableitung ( 2 ). The total pressure P in the heating steam space ( 11 ) was now high enough to allow the condensate into the existing steam condensate drain ( 2 ) could drain without a safety-critical condensate level ( 6 ).

It an energy consumption of approx. 6 t / h heating steam was measured.

The safety-related consideration of the example 1 Example 3 shows that only in example 3 was an ideal mode of operation possible for the existing plant for silane distillation.

When comparing the example 2 Example 4 also shows a significant improvement in the effectiveness of the silane distillation process. The inventive method led to an approximately 25% energy savings, since instead of the previously required about 8 t / h of water vapor in the process according to the invention only about 6 t / h of heating steam were necessary.

Claims (3)

Method for introducing energy to a product via a device for heat transfer by condensation of steam, characterized in that the occurring vapor pressure on the heating steam side of the device is kept greater than the back pressure of the condensate drainage system independently of the heating steam temperature by additional supply of inert gas on the heating steam side , Method according to claim 1, characterized in that the introduced inert gas selected is selected from the group containing helium, neon, argon, krypton, xenon, Radon, compressed air and nitrogen or mixtures thereof. Method according to claim 1 or 2, characterized in that steam is used as steam becomes.