WO2014191309A1

WO2014191309A1 - Apparatus for recovering reaction enthalpy

Info

Publication number: WO2014191309A1
Application number: PCT/EP2014/060626
Authority: WO
Inventors: Nicola FIOROTTO; Matteo GHENO
Original assignee: Versalis S.P.A.
Priority date: 2013-05-27
Filing date: 2014-05-23
Publication date: 2014-12-04
Also published as: ITMI20130857A1; TW201502445A

Abstract

An apparatus for recovering reaction enthalpy which comprises : - at least one reaction section which includes at least one primary distribution circuit for a utility fluid, - at least one heat-transfer device that includes at least one secondary distribution circuit for a service fluid, - at least one collecting header of said utility fluid; said apparatus characterized in that each primary distribution circuit is connected with at least one secondary distribution circuit by connection means, and characterized in that at least one flow-regulation device, having one inlet and two outlets, is installed on each secondary distribution circuit.

Description

APPARATUS FOR RECOVERING REACTION ENTHALPY

The present invention relates to an apparatus for recovering reaction enthalpy, in particular the reaction enthalpy available in production processes of polymeric resins.

In the present patent application, all the operating conditions indicated in the text should be considered as being preferred conditions even if not expressly specified.

For the purposes of the present document, the term

"comprise" or "include" also comprises the term "consisting in" or "essentially consisting of".

For the purposes of the present document, the definitions of the ranges always comprise the extremes unless otherwise specified.

A phase common to all production processes of polymeric resins is that of the preparation of the reagents to be fed to the reaction area. Additives such as initiators and/or reaction catalysts, chain transfer agents, dyes, are added, for example, in this area to the monomers which form the basic process reagents. Once the reagent mixture has been prepared, it must be heated to the ignition temperature, i.e. the temperature at which the possible initiator and/or catalyst is activated or the temperature at which the thermal polymerization of the monomers is initiated. In order to heat the reaction mixture to the ignition temperature, said mixture is normally fed to a heat exchanger. This exchanger can generally be heated either with steam or with diathermic oil preheated in an oven.

The use of steam or diathermic oil preheated in an oven excludes any possible form of thermal integration with the other sections of the plant.

If steam is used for performing the heating service, the energy used for generating the same steam Outside Boundary Limits (OSBL) , is supplied to the system. The steam is normally generated by burning natural gas or other fossil fuels.

If, on the other hand, diathermic oil coming from an oven is used, the combustion energy of the methane or other possible fuel fed to the oven, is transferred to the process stream.

These two solutions ensure that the heating section of the reagent mixture remains isolated and is not thermally integrated with the rest of the process, as the utility used for the heating comes either from OSBL or from a facility. Thermal recovery is not possible in either of these two options.

In principle, the reaction enthalpy could be recovered when the same service fluid (normally demineralized water or diathermic oil) which is used for the temperature control in the reaction section, is fed to the exchanger dedicated to heating the reagent mixture .

This operation, however, is not possible due to the pressure drops which are generated in the distribution circuit of the service fluid.

Traditionally, both when diathermic oil is used as utility fluid and also when demineralized water is used as utility fluid, the circuits for the temperature control inside the reactors (both for heating and cooling) are completely independent from the circuit for heating the reagent mixture. This configuration has the disadvantage of not allowing the use of the reaction enthalpy (exothermic) for heating the reagents. During the normal run of a polymerization plant, the utility fluid for the thermal control absorbs the reaction energy during its passage through the reactor. This energy potential could be recovered for performing a heating service at lower thermal levels than those of the reaction, but this is not possible due to the configuration of the service fluid circuit .

The Applicant, on the other hand, proposes a new configuration which has the advantage of allowing the reaction energy to be recovered, thus significantly improving the energy efficiency of the process.

In said configuration, the circuits for controlling the temperature inside the reactors are connected with the circuit for heating the reagent mixture. This does not create any operative or safety limit or complication for the plant running, since the maximum reliability of the temperature control inside the reactors and the linear operability of the system is always guaranteed.

The Applicant has therefore found a new apparatus characterized by a specific configuration of the distribution circuit of a utility fluid.

Said apparatus comprises:

at least one reaction section which includes at least one primary distribution circuit for a utility fluid,

at least one heat-transfer device that includes at least one secondary distribution circuit for a utility fluid,

at least one collecting header of said utility fluid;

said apparatus characterized in that each primary distribution circuit is connected with at least one secondary distribution circuit by connection means, and characterized in that at least one flow-regulation device, having one inlet and two outlets, is installed on each secondary distribution circuit.

The apparatus thus described allows to save the energy in the generation of the utilities used in the process industry (steam and hot diathermic oil) . In particular, in the production of polymeric resins based on styrene and styrene plus rubber (such as, for example, GPPS, HIPS and ABS) , the energy saving that can be reached by adopting this thermal integration system is 155% with respect to the total (result obtained in the HIPS plant of Dunastyr) .

Further objectives and advantages of the present invention will appear more evident from the following description and enclosed drawings, provided for purely illustrative and non-limiting purposes.

Figure 1 illustrates an embodiment of the present invention in which there is a reaction area (A) and an exchanger (B) , a three-way valve (C) , a primary distribution circuit header (D) , a secondary distribution circuit (E) , a collecting header (F) , a connecting duct (G) , an outlet duct which connects the three-way valve with the collecting header (H) , a connecting duct (I) between the primary distribution circuit and the duct (F) , a feeding duct of the reagents (L) , an outlet duct of the products (M) .

Detailed description

It is object of the present invention an apparatus for recovering reaction enthalpy which comprises:

- at least one reaction section which includes at least one primary distribution circuit for a utility fluid,

- at least one heat-transfer device that includes at least one secondary distribution circuit for a utility fluid,

- at least one collecting header of said utility fluid;

A further object of the present invention relates to a method for recovering reaction enthalpy which comprises the following steps:

transferring reaction enthalpy to a utility fluid which is circulating in a primary distribution circuit, regulating the temperature of the reaction products, and generating a heated utility fluid,

- transferring at least a part of said heated service fluid to at least a secondary distribution circuit which heats the reagents generating a cooled utility fluid,

regulating the outlet flow-rate of said cooled utility fluid by means of a regulation device having one inlet and two outlets.

The flow-rate of said utility fluid leaving a secondary distribution circuit can be the same as the flow-rate of the service fluid entering said secondary circuit .

A collecting header is a duct which carries the utility fluid from the utilities it has heated or cooled to the accumulation tank from which it was withdrawn for being sent to the various utilities.

Each primary circuit can be connected with one or more secondary circuits. The energy which the service fluid present inside the primary circuit can transfer when it enters the secondary circuits does not necessarily have to be sufficient for guaranteeing the contemporary completion of the heating services. Said secondary circuits can be run alternately or an additional utility fluid (of the same kind as those already used) coming from other plant sections or from OSBL, can be fed to said secondary circuits together with the utility fluid coming from the primary circuit. This additional utility fluid can have the function of supplying possible make-up energy necessary for completing the heating services.

Preferably the service fluid from the secondary circuits can be sent, after having performed dedicated heating services, to a further circuit in order to optimize the energy recovery. For this purpose, the collecting header of the service fluids is used.

The service fluid can be withdrawn from the collecting header in order to feed the secondary circuits.

In this case, it is absolutely necessary that the outlet of the service fluid from the secondary circuit be downstream of the inlet into the same circuit, otherwise thermal recovery execution would be jeopardized.

The circulation of the utility fluid in the secondary distribution circuits is guaranteed by a pump, preferably centrifugal. The regulation device having an inlet and two outlets is envisaged as being installed on the secondary circuits in the pump suction and downstream of the heat exchange device.

The service fluid downstream of the reaction section, therefore circulating in the primary circuit, may not have sufficient pressure for overcoming the pressure drops necessary for entering the secondary distribution circuits.

On the whole, the absolute pressures established in the distribution circuits of the utility fluids do not influence the functioning of the apparatus object of the present invention.

The entry or not of the service fluids into at least a second distribution circuit is in fact governed by the pressure difference established between the secondary circuit and the collecting header of the utility fluids. If the apparatus, object of the present invention, is not adopted, the thermal integration and therefore the recovery of reaction enthalpy cannot be effected, as the pump present in the secondary distribution circuits brings the same circuit to a higher pressure than that of the collecting header, thus preventing the first utility fluid, which is at a lower pressure but at a higher temperature, from entering the secondary circuit.

Under normal operating conditions, a service fluid coming from the reaction area is at a pressure P2, whereas the service fluid leaving the exchanger which heats the reagents, is at a pressure PI, which decreases as it moves towards the pump suction. Depending on how the general distribution circuit of the service fluid has been designed, the following situations can be created: P1>P2, P1=P2 and PKP2.

If P1>P2, the utility fluid in the collecting header (coming from the reaction area) will never be able to enter the secondary circuit which feeds the service fluid to the exchanger.

If P1=P2 and PKP2, the pressure drops which the utility fluid must overcome to be fed to the exchanger do not allow the passage of liquid (P2 is not sufficiently higher than PI as to overcome the pressure drops) .

The apparatus, object of the present invention, directs the flows of the service fluids in the desired directions. The regulation device present on the secondary circuits, in fact, diverts the flow leaving the exchanger towards the collecting header, whereas the connecting duct, free of flow-regulation devices, allows the service fluid to reach the secondary circuit in the fluid circulation pump suction.

If the same pump were to be removed in order to lower the pressure of the secondary circuits, there would be no circulation of fluid towards the heat- exchange device. The installation of a regulation valve, having an inlet and two outlets, therefore directs the service fluid univocally either towards the pump or towards the collecting header, ensuring, when required, the desired make-up of service fluid coming from the primary circuit.

The flow-regulation device having an inlet and two outlets is preferably a three-way valve, more preferably a three-way valve of the "trans-flow" type.

As already specified, said regulation device allows the utility fluid coming from the primary distribution circuit to be accurately directed towards a secondary distribution circuit, enabling a part of the flow-rate to be extracted from the secondary distribution circuit in order to send it to a collecting header of the utility fluids.

The flow-rate leaving the secondary distribution circuit can be substituted by an equal volumetric flow- rate of utility fluid coming from the primary distribution circuit. This portion can also be removed from the same header.

The reaction section preferably operates with an increasing temperature profile ranging from 80°C to 160°C. The heat-transfer device preferably brings the mixture of reagents from a storage temperature which ranges from 20°C to 30°C to an activation temperature of the polymerization reaction which ranges from 70°C to 90°C.

The implementation of the apparatus, object of the present invention, can lead to a saving of about 10% of the total energy required in a production plant of polymeric resins.

Claims

1. An apparatus for recovering reaction enthalpy which comprises :

- at least one reaction section which comprises at least one primary distribution circuit for a utility fluid,

at least one heat-transfer device which comprises at least one secondary distribution circuit for a service fluid,

- at least one collecting header of said utility fluid;

2. The apparatus according to claim 1, wherein the outlet of the service fluid from the secondary circuit is downstream of the inlet of the service fluid in the same circuit.

3. The apparatus according to claim 1 or 2, wherein the secondary distribution circuit comprises a pump and the regulation device having one inlet and two outlets, is installed at the pump suction and downstream of the heat-transfer device.

4. The apparatus according to any of the claims from 1 to 3, wherein the regulation device is a three-way valve .

5. The apparatus according to any of the claims from 1 to 4, wherein, when the utility fluid is removed by a collecting header, then the outlet of the service fluid from the secondary circuit is downstream of the inlet of the same circuit.

6. A method for recovering reaction enthalpy which comprises the following phases:

- transferring reaction enthalpy to a service fluid which is circulating in a primary distribution circuit, regulating the temperature of the reaction products, and generating a heated service fluid, - transferring at least a part of said heated utility fluid to at least a secondary distribution circuit which heats the reagents generating a cooled utility fluid,

7. The method according to claim 6, wherein the flow- rate of said utility fluid leaving a secondary distribution circuit is equal to the flow-rate of utility fluid entering said secondary circuit.

8. The method according to claim 6 or 7, wherein the utility fluid is removed by a collecting header.