EP0033093A2 - Process for dry cooling of coke - Google Patents

Abstract

In this process, gas-permeable bulk material with a strongly temperature-dependent coefficient of thermal conductivity is fed into a shaft-shaped chamber from above, in which it is treated in countercurrent with a gaseous cooling medium rising from the bottom. The cooling medium is supplied in two partial flows, the first partial flow being introduced into the lower part of the chamber, while the second partial flow is fed into an area of the chamber in which the bulk material to be cooled has at least one temperature (ϑG) above which the coefficient of thermal conductivity (λ) of the bulk material rises sharply depending on the temperature. The process is particularly suitable for dry coke cooling.

Description

Process for cooling gas-permeable bulk material.

The invention relates to a method for cooling gas-permeable bulk material with a temperature-dependent coefficient of thermal conductivity and a shaft-shaped chamber in which the bulk material applied from above is treated in countercurrent with a gaseous cooling medium rising from the bottom, the cooling medium being used in two partial flows.

It is known to cool bulk goods of various types by placing them from above into a shaft-shaped chamber through which a gaseous cooling medium, preferably air or inert gas, flows in counterflow to the flowing bulk material, the cold cooling medium normally being in the lower part initiated the chamber and the heated cooling medium is withdrawn from the top of the chamber. The heated cooling medium can then be cooled accordingly, if necessary with heat recovery in a heat exchanger, a waste heat boiler or other cooling device, and then returned to the feed point in the lower part of the shaft-shaped chamber.

In recent times, the method of operation described above has become particularly important for so-called dry coke cooling. The starting point for this development was the consideration that the method previously used in coking technology for coke cooling, in which the glowing coke is cooled by extinguishing with water in special extinguishing towers, is extremely unfavorable from the point of view of energy use or energy recovery and environmental protection. In this coke quenching, which has been customary to date, the amount of heat dissipated with the extinguishing water is discharged unused into the environment, ie in the form of vapor plumes into the air and / or with the extinguishing water running off.

On the other hand, if the method of operation described above is used, it is possible to recover a large part of the heat of the red-hot coke by cooling the gaseous cooling medium circulated in a waste heat boiler or the like.

It is therefore obvious that the so-called dry coke cooling is a preferred field of application of the present invention, but is not limited to this. However, it has been shown that the downward movement of the coke to be cooled in the shaft-shaped chamber can have different speeds. The gas flow through the cross section of the chamber is also uneven in many cases. Both of course also result in uneven cooling of the coke, which takes place more slowly, particularly in the upper part of the chamber.

For the dry quenching of coke, a device is already known from DE-AS 24 32 025 in which the gaseous Cooling medium is introduced into the cooling chamber in two partial flows. One partial flow is introduced into the fixed bed at the bottom of the chamber, while the second partial flow is led into the interior of the chamber via a so-called flow divider and exits into the fixed bed in the region of the center axis. However, no information is given in this publication about the special conditions under which the second partial flow of the cooling medium takes place or what the division of the partial flows should be. Rather, the device described there merely serves the purpose of achieving the most uniform possible movement of the material to be treated with the cooling medium being distributed as evenly as possible.

• 1. Herabsetzung des Druckverlustes des gasförmigen Kühlmediums in der Kammer.
• 2. Günstige Beeinflussung der Temperaturdifferenzen zwischen gasförmigem Kühlmedium und Feststoff.
• 3. Verbesserte Regelbarkeit sowohl im Hinblick auf die Menge des gasförmigen Kühlmediums als auch im Hinblick auf die Wärmeabfuhr aus dem zu kühlenden Schüttgut.

In contrast, the object of the invention is to bring about a general optimization in a method of the type described at the outset, in particular an improvement in the following points:

• 1. Reduction of the pressure loss of the gaseous cooling medium in the chamber.
• 2. Favorably influencing the temperature differences between gaseous cooling medium and solid.
• 3. Improved controllability both with regard to the amount of the gaseous cooling medium and with regard to the heat dissipation from the bulk material to be cooled.

The method used to achieve this object is characterized in that the first partial flow of the cooling medium is introduced into the lower part of the chamber in a manner known per se, while the second partial flow is fed into a region of the chamber in which the bulk material to be cooled is at least has a temperature (ϑ _G ) above which the thermal conductivity (λ) of the bulk material rises sharply depending on the temperature.

The invention is based on the knowledge that for certain solids, which include coke, the thermal conductivity (λ) is strongly temperature-dependent. The illustration in Fig. 1 therefore shows a coordinate system in which the temperature (ϑ) and the ordinate the thermal conductivity (λ) have been plotted on the abscissa. The typical curve profile shown in this coordinate system clearly shows that in such cases the coefficient of thermal conductivity (A) initially does not increase or increases very slowly with increasing temperature. Only when a certain limit temperature (ϑ _G ), which of course depends on the substance, is reached or exceeded, does the heat conductivity increase relatively steeply.

und somit stofflich bedingt, weil S die charakteristische Dicke des betreffenden Feststoffkörpers und dessen Wärmeleitzahl angibt.On the other hand, the time course of the convective total heat transport between the solid and the gaseous cooling medium is determined by the thermal conductivity in the solid itself and the heat transfer resistance between the solid and the gaseous cooling medium. Here the thermal resistance =

and thus materially because S the indicates the characteristic thickness of the solid body in question and its coefficient of thermal conductivity.

definiert, wobei durch die Wärmeübergangszahl α der Wärmeaustausch zwischen dem gasförmigen Kühlmedinm und den Oberflächen des Feststoffes beschrieben wird. Die Wärmeübergangszahl ist dabei abhängig von der Umströmung des Feststoffkörpers, das heisst von seiner geometrischen Form und der Strömungsgeschwindigkeit des gasförmigen Kühlmediums.The thermal resistance can therefore only be influenced by the geometric shape of the solid body. The heat transfer resistance, on the other hand, is included

defined, whereby the heat exchange between the gaseous cooling medium and the surfaces of the solid is described by the heat transfer coefficient α. The heat transfer coefficient is dependent on the flow around the solid body, that is to say on its geometric shape and the flow rate of the gaseous cooling medium.

während andererseits im Bereich oberhalb der Grenztemperatur (ϑ_G) die umgekehrte Beziehung gilt :

With regard to the temperature dependence of the coefficient of thermal conductivity (λ) described above, however, this means that the following relationship applies in the area below the limit temperature (ϑ _G ):

while on the other hand the reverse relationship applies in the area above the limit temperature (ϑ _G ):

) einstellt, der den Gesamtwärmetransport bestimmt. Es ist deshalb nicht zweckmässig, bereits die Gesamtmenge des gasförmigen Kühlmediums in den Unterteil der schachtförmigen Kammer einzuleiten, da dort nicht der ihrer Menge entsprechende Kühleffekt erzielt wird. Es genügt vielmehr, wenn in den Unterteil der Kammer ein Teilstrom des gasförmigen Kühlmediums eingeleitet wird, der gerade ausreicht, um die dort vorhandene Wärme abzuführen. Es ist für den Kühleffekt vielmehr besser, wenn der zweite Teilstrom des gasförmigen Kühlmediums in den oberen Bereich der schachtförmigen Kammer eingeleitet wird, in dem das zu kühlende Schüttgut noch eine Temperatur aufweist, die nicht unterhalb der sogenannten Grenztemperatur ( ϑ_G) liegt, weshalb der Wärmeleitwiderstand (

) dort entsprechend klein ist.In practice, however, this means that in the lower part of the shaft-shaped chamber there is a lower coefficient of thermal conductivity (α) due to the strong cooling of the bulk material there, and thus a high thermal conductivity (

) that determines the total heat transfer. It is therefore not advisable to use the total amount of the gaseous cooling medium to be introduced into the lower part of the shaft-shaped chamber, since the cooling effect corresponding to their quantity is not achieved there. Rather, it is sufficient if a partial flow of the gaseous cooling medium is introduced into the lower part of the chamber, which is just sufficient to dissipate the heat present there. Rather, it is better for the cooling effect if the second partial flow of the gaseous cooling medium is introduced into the upper region of the shaft-shaped chamber, in which the bulk material to be cooled still has a temperature that is not below the so-called limit temperature (ϑ _G ), which is why Thermal resistance (

) is correspondingly small there.

It has proven to be expedient that, according to the invention, about 20 to 50% by volume of the total amount of the cooling medium required is added with the second partial flow.

) zur Folge hat. Konstruktiv lässt sich das dadurch herbeiführen, dass entweder die schachtfömige Kammer in ihrem oberen Teil eine entsprechende Verjüngung aufweist, oder es werden im Oberteil der Kammer entsprechende Einbauten angebracht.This measure can also be supported by the fact that in the area of the feed point of the second partial flow of the cooling medium, the flow velocity of the media is increased by a corresponding narrowing of the flow channel, which additionally reduces the heat transfer resistance (

) results. In terms of construction, this can be brought about by either having a corresponding taper in the upper part of the shaft-shaped chamber, or by installing appropriate internals in the upper part of the chamber.

When using the method according to the invention for dry coke cooling, the second partial stream of the gaseous cooling medium should According to the invention, be placed in a region of the chamber in which the coke to be cooled has a temperature of approximately 400 to 600 ° C.

This mode of operation will be explained below as an exemplary embodiment using the flow diagram shown in FIG. 2. The red-hot coke is fed into the shaft-shaped chamber 6 from above into the shaft-shaped chamber 6 at a temperature of approx. 1 100 ° C. in an amount of approx. 80 t / h and initially reaches the uppermost part above the line 3, which is also known as Antechamber 13 is called. In the pre-chamber 13, the fluctuations that may occur during the supply of the glowing coke are to be compensated for, so that quasi-stationary conditions can develop in the areas of the chamber 6 underneath. The entire chamber 6 is provided with a suitable refractory lining and has a taper in its upper region II, through which the flow velocities of the media in this region are correspondingly increased compared to the lower region 1.

The filled coke forms the fixed bed 7 in the chamber 6, which is shown hatched in the figure. The temperature inside the fixed bed decreases steadily from top to bottom, so that the cooled coke can be drawn off at a temperature of approx.

According to the invention, the gaseous cooling medium is introduced into the chamber 6 in two partial flows, the first partial flow entering the lower part of the chamber 6 via the line 1. At the same time, the second partial flow in an amount of about 30-35% by volume of the total amount is introduced into the chamber 6 via the line 2 in a region in which the fixed bed 7 has a temperature of approximately 500 ° C. In this temperature value according to the invention conditions are fulfilled with respect to the limiting temperature (θ _G) de _'r thermal conductivity (λ).

Above the feed point for the second partial flow of the gaseous cooling medium, the thermal conductivity in the fixed bed 7 is smaller than the heat transfer resistance, while below the feed point the conditions are exactly the opposite.

This is represented by the formula in the figure in FIG. 2.

The heated gaseous cooling medium is withdrawn via the line 3 from the upper part of the chamber 6 and reaches the waste heat boiler 4, in which the necessary cooling takes place with heat recovery. The cooled gaseous cooling medium can then be recirculated to line 1 via line 9 and blower 10. Line 2 branches off from this. The control flaps 11 and 12 are used for the necessary adjustment of the two partial flows. Instead of the butterfly valves 11 and 12, fans can also be used to regulate the two partial flows. Likewise, instead of the heat return Extraction in the waste heat boiler also conceivable other possibilities for heat recovery, in which the recovered energy is used, for example, for preheating the coking coals or as process heat. Inert gas, preferably flue gas, is used as the gaseous cooling medium. As can be seen from the illustration in FIG. 2, the tapering of the chamber 6, through which the flow velocities in the upper part thereof are to be increased, begins in the region of the entry point of the line 2 into the chamber 6. This is of course a pure one Contingent measure that is not always necessary.

• 1. Der Druckverlust für die Durchströmung der Kammer wird herabgesetzt, da der Gasstrom aufgeteilt wird und somit nicht die gesamte Gasmenge durch das gesamte Schüttgut gedrückt werden muss. Hieraus resultiert ein verringerter Energiebedarf für das Gebläse.
• 2. Die Temperaturdifferenzen zwischen Gas und Feststoff werden günstig beeinflusst.
• 3. Durch die Aufteilung in Teilströme wird die Gasmenge besser regelbar, was wiederum eine verbesserte Regelbarkeit der Wärmeabfuhr aus dem Festbett zur Folge hat.

The advantages of the method according to the invention can be summarized as follows:

• 1. The pressure loss for the flow through the chamber is reduced since the gas flow is divided and therefore the entire amount of gas does not have to be pressed through the entire bulk material. This results in a reduced energy requirement for the blower.
• 2. The temperature differences between gas and solid are influenced favorably.
• 3. The division into partial flows makes the amount of gas more controllable, which in turn results in improved controllability of the heat dissipation from the fixed bed.

Claims (4)

1.Procedure for cooling gas-permeable bulk material with a strongly temperature-dependent coefficient of thermal conductivity in a shaft-shaped chamber, in which the bulk material fed in from above is treated in countercurrent with a gaseous cooling medium rising from the bottom, the cooling medium being used in two partial flows , characterized in that the first partial flow of the cooling medium is introduced into the lower part of the chamber in a manner known per se, while the second partial flow is introduced in a region of the chamber in which the bulk material to be cooled has at least one temperature (ϑ _G ), Above which the thermal conductivity (λ) of the bulk material rises sharply depending on the temperature. 2. The method according to claim 1, characterized in that in the area of the feed point of the second partial flow of the cooling medium, the flow rate of the media is additionally increased by a corresponding narrowing of the flow channel. 3. The method according to claims 1 and 2, characterized in that about 20 to 50 vol. _{% Of} the total amount of cooling medium required are added with the second partial flow. 4. Application of the method according to claims 1-3 to the so-called dry coke cooling, characterized in that the second partial flow of the cooling medium is applied in a region of the chamber in which the coke to be cooled has a temperature of approximately 400 to 600 ° C having.

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