EP4305129B1 - Method and apparatus for steam cracking - Google Patents

Description

The present invention relates to a process and a plant for steam cracking according to the preambles of the independent claims.

Background of the invention

The present invention relates to steam cracking (steam cracking, thermal cracking, steam cracking, etc.) used to produce olefins and other basic chemicals, and which is described, for example, in the article " Ethylene" in Ullmann's Encyclopedia of Industrial Chemistry, online publication of 15 April 2009, DOI: 10.1002/14356007.a10_045.pub2 , is described. For the terms used below, reference is also made to the relevant specialist literature.

In steam cracking, the heat energy required to initiate and maintain the endothermic reactions is typically provided by the combustion of heating gas in a combustion chamber, which forms the so-called radiation zone of a cracking furnace, and through which so-called coils (cracked tubes) are passed, through which a hydrocarbon-steam mixture to be converted is passed to obtain a product mixture, the so-called raw or cracked gas. In the most common applications, the combustion air required for combustion is fed into the radiation zone without preheating (so-called natural draft) and burned there together with the heating gas. A simplified representation is shown in the attached Figure 1 which is explained below with the corresponding reference numerals.

A in Figure 1 The cracker furnace 10 shown or a corresponding furnace unit (also referred to here as cracking furnace or furnace for short) has the radiation zone 11 and a convection zone 12. A steam cracking plant can contain several corresponding cracker furnaces 10. Plant components or units referred to below as central are available to several cracker furnaces 10, decentralized units are provided separately for each cracker furnace 10.

By means of a central feed preheater 20 shown as an example and a central process steam generator 30, a hydrocarbon feed H is heated and process steam P is provided, which is heated in the convection zone 12 in a manner known per se (see in particular also Figure 4 ) are further heated, combined to form a feed stream F and then fed to the radiation zone 11. The representation according to Figure 1 is, as mentioned, greatly simplified and merely exemplary. For example, in a so-called pass control, a corresponding feed stream can be divided into several partial streams in the area of the convection zone 12, which can then be preheated separately from one another and finally guided through groups of, for example, six or eight split tubes in the radiation zone 11. Here and below, centralized units can be replaced by decentralized units and vice versa at any time.

The cracked gas C is taken from the radiation zone 11 and is cooled by means of one or more cracked gas coolers 13, which can be designed in particular as known quench coolers or can include such quench coolers and which can also function as steam generators, and is then fed to a central cracked gas separation and cracked gas processing 90. Further details on corresponding quench coolers, which can be designed in particular as classic quench coolers or so-called linear quench exchangers (LQE), are explained below. The invention is not limited by a specific embodiment.

A central feed water system 40 is used to provide feed water W, which in the example shown is also heated in the convection zone 12 and is then further heated by means of one or more cracked gas coolers 13 to obtain high-pressure or super-high-pressure saturated steam S (hereinafter also referred to as saturated steam for short) and finally evaporated. In the example shown, the saturated steam S is superheated in the convection zone 12 to obtain superheated high-pressure steam or superheated super-high-pressure steam T (hereinafter also referred to simply as superheated steam) and fed into a central steam system 50.

By means of a central heating gas system 60, which is followed by a possible central heating gas preheating 65, in which process or auxiliary materials such as superheated steam at high, medium or low pressure, washing water and/or quench oil, but also electrical current as heating media or heat sources is used, feed heating gas Y is heated to preheated heating gas X and fed to the radiation zone 11 or to burners not separately shown therein.

In the embodiment illustrated here, combustion air L reaches the radiation zone 11 or the burners there via an air intake 79. Flue gas Z is discharged from the radiation zone 11, passes through the convection zone 12 and is then discharged into a flue gas treatment system or to a central or decentralized chimney 80 with or without a fan and is then released into the atmosphere.

In the Figure 1 The central heating gas preheating 65 illustrated is optional. Decentralized heating gas preheating (ie separate for the individual cracker furnaces 10 or furnace units) is also possible. The same applies to the feed preheating and the process steam generation, which can also be implemented decentrally as an alternative to the centralized implementation.

It is known from the state of the art that preheating the combustion air can be used as an efficiency-enhancing measure to save heating gas and thus reduce energy consumption and carbon dioxide emissions. Corresponding designs are described in the Figures 2 and 3 shown, where Figure 2 a central and Figure 3 a decentralized combustion air compression 70 and combustion air preheating 75.

In general, the term "increase in efficiency" can be understood here in particular as an increase in the so-called specific efficiency, which in turn is understood to mean the proportion of the heating gas energy introduced that is found in the products formed, in this case the cracked gas. This differs from the so-called thermal efficiency, i.e. the proportion of the under-firing output that is found in the products and other media (cracked gas or steam), or, in other words, the proportion that is not lost as heat to the environment (via chimney, warm surfaces, leaks). The specific efficiency is increased by air preheating because less under-firing is required for the same amount of cracked gas. The thermal efficiency, on the other hand, does not necessarily increase through the use of air preheating, as this may also be limited by a minimum flue gas discharge temperature, see below.

In the following, centrally and decentrally arranged units are provided with the same reference numerals. The type of arrangement results from the illustrated positioning inside or outside the respective cracker furnace 10 or the furnace unit, with a decentralized arrangement being present when positioned inside and a central arrangement when positioned outside. For example, central combustion air compression 70 can also take place with decentralized combustion air preheating 75. The combustion air is also referred to below as air for short, and its preheating is also referred to as air preheating for short.

In air preheating, for example, superheated or, depending on the application, non-superheated steam at high, medium or low pressure, wash water and/or quench oil can be used as heating media or electricity can be used as a heat source. The use of directly transferred heat from the exhaust gas flow Z as a heat source is also possible. The use of superheated high-pressure or super-high-pressure steam T shown in the figures is optional and is carried out depending on the selected preheating temperature.

To summarize, the preheated combustion air can be provided centrally or decentrally. Depending on availability and the desired preheating temperature, the heating media used can be (superheated) super high pressure steam (SHD), (superheated) high pressure steam (HD), (superheated) medium pressure steam (MD), (superheated) low pressure steam (ND), saturated steam, wash water or quench oil, for example from a central cracked gas separation and cracked gas treatment, or flue gas after leaving the convection zone, typically in a decentralized arrangement of the air preheating.

Low-pressure steam is generally understood to mean steam at a pressure level of 1 to 10 bar absolute pressure (abs.), in particular 4 to 8 bar (abs.); medium-pressure steam is understood to mean steam at a pressure level of 10 to 30 bar (abs.), in particular 15 to 25 bar (abs.); high-pressure steam is understood to mean steam at a pressure level of 30 to 60 bar (abs.), in particular 35 to 50 bar (abs.); and super-high-pressure steam is understood to mean steam at a pressure level of 60 to 175 bar (abs.), in particular 80 to 125 bar (abs.). If high-pressure steam is referred to below for short, this should also be understood to mean super-high-pressure steam.

The term super-high pressure level refers to the pressure level specified for super-high pressure steam, regardless of whether this is specified for the steam itself or, for example, for feed water used to form the steam. The same applies to the terms high pressure level, medium pressure level and low pressure level.

To provide the pressure level required for the flow through the air preheaters used in the air preheating system or to compensate for a corresponding pressure loss, the air drawn in from the atmosphere can be compressed by means of a driven fan in the air compression system, either centrally or decentrally. Alternatively, it is also possible to use a fan arranged downstream of the air preheating system, which creates a corresponding suction.

Air preheating is used in connection with steam cracking, for example in the US 3,426,733 A , the EP 0 229 939 B1 and the EP 3 415 587 A1 described, as well as in connection with air preheating in boilers, for example in the EN 10 2004 020 223 A1 and the WO 2013/178446 A1 .

From the US 4,321,130 A It is known that combustion air can be preheated prior to introduction into a cracking furnace in a system for the pyrolytic conversion and separation of hydrocarbons by means of bottoms, overhead and/or quench water streams discharged from a primary fractionation unit externally connected to the pyrolysis reactor in order to optimize the thermal efficiency of the overall process.

The US 2020/172814 A1 discloses a cracking furnace system for converting a hydrocarbon feedstock into cracked gas, the cracking furnace system comprising a convection section, a radiant section, and a cooling section, the convection section including a plurality of convection banks configured to receive and preheat the hydrocarbon feedstock, the radiant section including a furnace comprising at least one radiant coil configured to heat the feedstock to a temperature enabling a pyrolysis reaction, the cooling section including at least one transfer line heat exchanger.

Air preheating generally improves heat transfer in the radiation zone and reduces the furnace's fuel requirements. This means that, for the same furnace load (here in particular understood as the same amount of hydrocarbons used and the same gap sharpness, which results in the same product flow), less combustion power is required overall and at the same time a larger relative proportion of the exhaust gas energy is transferred to the process gas. On the one hand, this means that the exhaust gas mass flow is reduced, which reduces combustion emissions and the residual heat released from the chimney to the atmosphere. On the other hand, it means that the amount of heat remaining in the flue gas at the outlet of the radiation zone is significantly reduced compared to a non-preheated furnace.

However, as preheating temperatures increase, this leads to difficulties in the design and operation of the downstream convection zone. In this zone, the hydrocarbon feedstock to be cracked and the associated process steam are preheated to temperatures of 550 to 700°C. In addition, boiler feed water fed to the furnace at high or super-high pressure level is normally preheated at 100 to 110°C in the convection zone, evaporated in the cracking gas cooler and finally superheated in the convection zone.

The reduced availability of exhaust gas heat in the convection zone results in the difficulty at high air preheating temperatures that, at the same furnace load, the required preheating power for the hydrocarbon feed and the process steam, as well as the required superheating power for the saturated steam flow generated unchanged in the cracked gas cooler, are almost constant. The lack of exhaust gas heat is therefore noticeable in the feed water preheating, which must be partially restricted. In addition, the inlet temperatures of the flue gas in the upper convection bundles in the convection zone, i.e. the heat exchange units arranged here for transferring heat from the flue gas to the media to be heated, drop significantly compared to the non-preheated furnace. Due to the decreasing temperature gradients, the area required by the convection bundles is therefore significantly larger, which requires more construction work.

In the EP 3 415 587 A1 This problem is to be solved, for example, by a heat pump system or by feeding non-preheated feed water into the steam drum. However, the solutions proposed there lead to high additional equipment costs due to the required heat pump and/or to significantly modified designs of the cracked gas cooling and steam generation, for which proof of long-term operability has not yet been provided.

The present invention is therefore intended to provide solutions that enable economical, efficient and practically feasible operation of a steam cracking plant.

Disclosure of the invention

Against this background, the present invention proposes a method and a plant for steam cracking according to the preambles of the independent claims. Advantageous embodiments are the subject of the dependent patent claims and the following description.

The present invention enables an extremely compact design of the convection zone, considered here as the sum of the heights of the individual convection bundles in the flue gas channel, a simple design of the chimney ducts downstream of the convection zone and maximum flue gas heat utilization, i.e. low flue gas outlet temperature at the chimney. Furthermore, a minimum fuel requirement can be achieved with the maximum possible production of superheated high-pressure or super-high-pressure steam.

The core of the present invention is the use of feed water, i.e. water that is subsequently used to generate (super) high-pressure steam, for the preheating of combustion air.

The measures proposed according to the invention, which lead to an intermediate cooling of feed water, contradict the common practice of aiming for maximum feed water preheating in the production of steam from combustion plants. In the context of the present invention, a deliberate maximum steam generation is dispensed with in order to achieve maximum energy recovery from the flue gas with minimal additional construction effort. The reduction in steam production is particularly advantageous in light of future designs of steam cracking plants, as this enables increased use of preferably so-called green electricity to drive machines. In this way, the plant's overall carbon dioxide emissions can be reduced even further. The combustion input is minimized with maximum energy yield from the remaining combustion of fossil fuels.

While in a pure steam boiler application only the fuel utilization rate for steam generation is to be optimized, the situation is much more difficult in a steam cracking furnace. Here, after the chemical conversion of the feedstock, steam generation is only the secondary task or a requirement in order to utilize the heat quantities generated. Accordingly, the use of the measures according to the invention in the steam cracking furnace not only influences the overall fuel utilization rate, but also in particular the distribution between chemical process utilization and steam generation. Therefore, measures that are provided for pure steam boilers cannot simply be transferred to steam cracking plants.

In further embodiments according to the invention and not according to the invention, alternatively or in addition to the measures proposed according to the invention, use of the furnace's own (super) high-pressure saturated steam as a heating medium in air preheating, a combined use of feed water and (super) high-pressure saturated steam as heating media in air and/or heating gas preheating, a use of (super) high-pressure saturated steam as a heating medium for process steam superheating, and a use of (super) high-pressure saturated steam as a heating medium for feed preheating or a combined use of (super) high-pressure saturated steam as a heating medium for process steam superheating and feed preheating can be carried out.

The present invention is based on a process for the conversion of one or more hydrocarbons by steam cracking, in which one or more feed streams containing the one or more hydrocarbons are steam cracked to obtain one or more product streams, ie cracked gas streams or Raw gas streams are passed through one or more radiation zones of one or more cracker furnaces, in which the one or more radiation zones are heated by firing heating gas with combustion air, in which at least part of the combustion air is subjected to combustion air preheating, in which steam is generated from feed water, and in which the feed water is subjected to feed water preheating in one or more convection zones of the one or more cracker furnaces. As mentioned, the feed streams can also be passed in one or more convection zones in parallel, e.g. according to the division into several groups of cracking tubes in the radiation zone.

According to the invention, as already mentioned, the combustion air preheating is carried out using heat which is extracted from at least a portion of the feed water upstream of the feed water preheating.

The invention therefore includes supplying cooled feed water to the convection zone of the furnace or furnaces, whereby the greatest possible cooling and thus the energetic use of the flue gas can be achieved. There are various variants for cooling the feed water, in which the heating gas quality in particular can be taken into account to avoid corrosion in the exhaust gas tract. In addition to using the feed water supplied to the furnaces as a heating medium in a central or decentralized air heating system, the feed water can also, as explained below, additionally or alternatively according to non-inventive embodiments, be used as a heating medium in a central or decentralized heating gas preheating system. Cooling can alternatively and according to non-inventive embodiments take place outside the furnace process.

The feed water preheating can be carried out in particular in such a way that only a first part of the feed water, which can be adjusted in particular, is used in one or more combustion air preheaters for heat exchange with at least a part of the combustion air to be heated and optionally in one or more heating gas preheaters for heat exchange with at least a part of the heating gas to be heated and a second part of the feed water, which can be adjusted in particular, is guided as a bypass flow around the combustion air preheater and possibly the heating gas preheater. The first and second parts can subsequently recombined and then fed to the feed water preheating in the convection zone.

In particular, if the first and/or second part of the feed water is adjustable, the temperature of the feed water at the inlet to the convection zone can be regulated in this way. The latter can be used in particular during operation to control the outlet temperature of the flue gas in the chimney. In such a process, the latter depends heavily on the temperature of the feed water.

With such a temperature control it is therefore possible, in particular, to increase the flue gas temperature during operation, especially temporarily, e.g. in the case of a changing heating gas composition, which could lead to a risk of corrosion if the flue gas partially condenses. In this case, less air preheating is achieved via feed water, the corresponding output can be compensated by subsequent air preheating stages, or by increasing the amount of fuel added to the furnace. In the optimal operating case with a preferred heating gas composition, a maximum preheating output is aimed for using feed water, which also leads to maximum flue gas heat utilization.

In other words, the temperature of the flue gas can be adjusted by adjusting a proportion of the feed water used in the air preheating and optionally also the heating gas preheating, which can be done in particular on the basis of a temperature of a flue gas to be achieved or detected in the convection zone downstream of the feed water preheating.

In general, the present invention is used in a process in which the steam generated from the feed water comprises superheated or non-superheated high-pressure or super-high-pressure steam which is formed from the feed water downstream of the feed water preheating. At least a portion of the feed water can be subjected to feed water evaporation after the feed water preheating using heat which is extracted from at least a portion of the one or more product streams, in particular in one or more cracked gas or quench coolers, to obtain high-pressure or super-high-pressure saturated steam. At least a portion of the high or super high pressure saturated steam can then be subjected to steam superheating in one or more convection zones to obtain the (superheated) high or super high pressure steam. For further details, please refer to the explanations of the Figures 1 to 4 referred to.

In general, within the scope of the present invention, the combustion air preheating can be carried out using heat that is extracted from a portion of the (superheated) high-pressure or super-high-pressure steam. In embodiments according to the invention, this is done in addition to using the heat of the feed water, and in non-inventive embodiments, it is done as an alternative thereto.

As already mentioned several times, the heating gas can be subjected to heating gas preheating, which can also be carried out using heat that is extracted from at least part of the feed water upstream of the feed water preheating. In embodiments according to the invention, this takes place in addition to the combustion air preheating and can take place as an alternative thereto in embodiments not according to the invention.

Within the scope of the present invention, the feed water preheating takes place in one or more flue gas ducts in the one or more convection zones, wherein the feed water preheating is carried out in particular at a lower temperature level than is carried out for steam superheating to obtain the superheated high or super high pressure steam, process steam heating to provide process steam that is used to form the one or more feed streams, and a large part of the feed heating of the one or more feed streams. In particular, the feed water preheating takes place near the end or at the very end of the flue gas duct from which the correspondingly cooled flue gas then flows out, i.e. at a point downstream (in the flow direction of the flue gas) at most one further heat recovery from the flue gas takes place. In this way, the outlet temperature of the flue gas from the convection zone can be controlled particularly advantageously.

Within the scope of the invention, the feed water can be heated to a temperature level of 80 to 140°C, in particular by means of a central or decentralized feed water system, and the feed water can be cooled to a temperature level of 40 to 100°C, to 95°C, to 90°C or to 85°C during combustion air preheating.

Within the scope of the present invention, the feed water of the combustion air preheating can be supplied at a pressure level of 30 to 60 bar (abs.), in particular of 35 to 50 bar (abs.), or of 60 to 175 bar (abs.), in particular of 80 to 125 bar (abs.), and can be subjected to the feed water preheating at this pressure level without additional pressurization. Alternatively, the feed water can be supplied to the combustion air preheating at a pressure level of 20 to 60 bar (abs.), in particular between 25 to 50 bar (abs.) or between 30 and 40 bar (abs.) and then, after additional pressurization, subjected to the feed water preheating at a pressure level of 30 to 60 bar (abs.), in particular from 35 to 50 bar (abs.), or from 60 to 175 bar (abs.), in particular from 80 to 125 bar (abs.). In the latter case, the feed water can advantageously be brought to an appropriate pressure by means of one or more pumps after the combustion air preheating.

The air can therefore be preheated directly with feed water at a (super) high pressure level, so that the intermediately cooled feed water can then be fed directly to the convection zone. Alternatively, the air can also be preheated with feed water at a reduced pressure level, as explained. The latter leads to a significantly lower design pressure of the associated air preheater and thus to less construction effort for this device.

Within the scope of the present invention, as also already mentioned, in particular a plurality of cracker furnaces can be used which are supplied with the feed water by means of a central feed water system, wherein the combustion air preheating can be carried out separately for each of the plurality of cracker furnaces (decentralized combustion air preheating) or jointly for the plurality of cracker furnaces (centralized combustion air preheating).

Embodiments according to the invention and not according to the invention are described below and in particular with reference to the Figures 5 to 22 explained further.

In all embodiments of the present invention, the combustion air preheating can be carried out in particular in several stages, whereby, for example, in a first stage, feed water can be used as the heating medium, in a second stage, medium-pressure steam can be used as the heating medium, and in a third stage, saturated or superheated (super) high-pressure steam can be used as the heating medium.

Other possible heating types or heating media (including electrical current) can also be used. Furthermore, more or fewer preheating stages than those mentioned can be provided. It is also possible to reuse the draining heating medium (in particular condensate formed) in previous stages (i.e. at a lower temperature level) in whole or in part, preferably immediately at the same pressure level in a heat exchanger in which the previously formed condensate is further subcooled, or after partial relaxation to a reduced pressure level and addition of superheated steam at this reduced pressure level. It may also be advantageous to return condensate to the steam generation either by arranging it at the appropriate height (above the steam drum, i.e. natural circulation) or by increasing the pressure (e.g. using a pump).

The appropriately cooled feed water is then fed into the convection zone, but at a noticeably reduced temperature.

The invention also relates to a plant for converting one or more hydrocarbons by steam cracking, the features of which, as mentioned, are reproduced in the corresponding independent patent claim.

With regard to the system provided according to the invention and its features, express reference is made to the above explanations regarding the method according to the invention, since these relate to a corresponding system in the same way. The same applies in particular to an embodiment of a corresponding system, which is advantageously set up to carry out a corresponding method in any desired embodiment.

The measures according to the invention and not according to the invention described in the context of the present application make it possible, when used individually or preferably in combination, to measurably improve the construction effort and/or the energy efficiency of steam cracking furnaces with air preheating, as explained again below with reference to specific examples.

A first of the effects of the individual measures is shown in Table 1. The first comparison system is a furnace with the same hydrocarbon load without air preheating, but with central heating gas preheating (reference A, 100% basis for relative comparison of the evaluation variables). The second comparison system is a furnace with the same hydrocarbon load with air preheating and with central heating gas preheating, but not designed according to the features of the present invention (reference B). All cases with air preheating listed in Table 1 are based on a resulting combustion air temperature of 248°C at the inlet of the radiation zone. The variants indicated with 1F, 2A, 3B, 4B, 5B and 6B are explained with reference to the figures and represent variants according to the invention and non-inventive variants. <b>Table 1 - Comparison of effectiveness for air preheating temperature of 248°C</b> Variant of the invention/reference Ref. A Ref. B Example 1F** Example 2A* Example 3B** Example 4B** Example 5B** Example 6B** Temperature of combustion air °C 15 248 248 248 248 248 248 248 Relative summed bundle height % 100% 136% 141% 86% 108% 92% 106% 91% Relative fuel consumption % 100% 78% 78% 78% 78% 78% 78% 78% Temperature of the flue gas at the outlet °C 119 138 89 189 91 91 91 91 Rel. super high pressure steam export from furnace % 100% 64% 73% 59% 61% 59% 61% 58% *: Design without use of feed water in air preheating
**: Version with use of feed water in air preheating

All variants marked with the suffix ** in Table 1 are designed according to the invention, since feed water is provided as the heating medium for air preheating.

The fundamental advantage of air preheating is evident when comparing reference A with reference B, in the form of a 22% reduction in fuel consumption. The same comparison shows that additional measures are required for air-preheated furnaces to compensate for the increased construction effort (in the form of the total bundle height) and the reduction in furnace efficiency (in the sense of the thermal efficiency described above) associated with the increasing flue gas outlet temperature. The inventive designs described below aim to compensate for these two disadvantages simultaneously and as well as possible.

Comparing variant 1F with reference B shows that the use of feed water for air preheating, with subsequent feeding into the convection zone at a reduced temperature level (according to the invention, hereinafter referred to as measure 1) leads to a significantly reduced flue gas outlet temperature and thus to improved furnace energy efficiency. The additional construction effort that has to be accepted in return is very low, with an increase of 5 percentage points, while the outlet temperature is reduced by just under 50 K. A similar result can be seen when comparing variants 2A and 3B. These two comparisons clearly underline the effectiveness of measure 1, which makes it possible to achieve significant improvements in furnace efficiency with little additional construction effort.

Another major advantage of measure 1 is the simple design of the flue gas flow after it leaves the convection zone. This is very similar to that of a furnace without air preheating, and is therefore much simpler than using a direct heat exchanger between the exhaust gas flow and the combustion air, where large-volume pipe arrangements and heat exchange surfaces have to be installed in the flue gas path of each individual furnace. Measure 1 produces a similar process effect, namely the transfer of exhaust gas heat to the combustion air, but indirectly using a heat carrier already present in the furnace area (feed water), which requires significantly smaller pipe cross-sections due to its liquid state.

A further advantage is the possible temperature control via the bypass system described, so that, in contrast to a system with direct heat exchange between combustion air and exhaust gas flow, the exhaust gas temperature can be easily adjusted/changed during operation. This means that fluctuations in the heating gas quality can be handled much better, see previous description.

The effect of air preheating with (super) high-pressure saturated steam (measure 2 not according to the invention in itself) can be illustrated by comparing variants 1F and 2A. By removing (super) high-pressure saturated steam before the superheater bundles for (super) high-pressure steam, proportionately more exhaust heat is available for the bundles located further downstream in the flue gas path. The temperature differences in the bundles increase, which greatly reduces the area required and the resulting height of the convection zone. The sole application of measure 2 therefore leads to a significant minimization of the construction effort, but at the same time the energy efficiency of the furnace decreases, since the flue gas outlet temperature increases by 100 K.

It follows that measures 1 and 2 have somewhat opposite effects. However, by comparing reference B with example 3B, it is very clear that a combination of measures 1 and 2 (referred to as measure 3 according to the invention) leads to a simultaneous improvement of the furnace in terms of construction effort and energy efficiency.

The comparison of variant 3B with variant 4B shows the effect of additional process steam superheating with (super) high-pressure saturated steam (measure 4 not according to the invention in itself). Similar to measure 2, this extraction of saturated steam and its use for process steam superheating leads to a reduction in construction costs, which in the given example leads to a consistent furnace energy efficiency by combining measures 1 (according to the invention) and 2 (not according to the invention in itself).

The comparison of variant 3B with variant 5B shows the effect of additional preheating with (super) high pressure saturated steam (not Inventive measure 5). Similar to measures 2 and 4 (each considered individually not inventive), this extraction of saturated steam and its use for preheating the feed leads to a reduction in construction costs, which in the given example 5B leads to a constant furnace energy efficiency through the simultaneous application of measures 1 (inventive) and 2 (considered individually not inventive).

The comparison of variant 4B or variant 5B with variant 6B shows the effect of the joint application of process steam superheating and feed preheating with (super) high-pressure saturated steam (measure 6 not according to the invention in itself). The maximum extraction of saturated steam and its use for process steam superheating and feed preheating leads to a maximum reduction in construction costs, which in the given example leads to a consistent furnace energy efficiency as in variants 3B, 4B, and 5B through the simultaneous application of measures 1 (according to the invention) and 2 (not according to the invention in itself).

The variants listed in Table 1 use different designs of the air preheater sequences, with three stages, with use of wash water, medium pressure steam and/or superheated (super) high pressure steam in addition to the explained use of feed water and/or (super) high pressure saturated steam.

As an additional illustration of the effectiveness of the claimed measures, Table 2 shows results for designs of various variants with even higher air preheating (300°C) and correspondingly even lower fuel consumption. The described effects of the measures remain unchanged. The comparison of variants 4A* with 4B* shows the positive influence of measure 2 on the construction costs. The comparison of example 4B* with 4B** shows the added value in terms of furnace efficiency when adding measure 1. <b>Table 2</b> - <b>Comparison of effectiveness for air preheating temperature of 300°C</b> Variant of the invention/reference Ref. A Ref. B Example 4A* Example 4B* Example 4B** Example 6B** Example 6C** Temperature of combustion air °C 15 248 300 300 300 300 300 Relative summed bundle height % 100% 136% 158% 109% 116% 111% 117% Relative fuel consumption % 100% 78% 73% 73% 73% 73% 73% Temperature of the flue gas at the outlet °C 119 138 119 118 88 89 89 Rel. super high pressure steam export from furnace % 100% 64% 55% 56% 56% 55% 57% *: Design without use of feed water in air preheating
**: Version with use of feed water in air preheating

All variants marked with the suffix ** in Table 2 are designed according to the invention, since feed water is provided as the heating medium for air preheating.

It is generally evident that at higher preheating temperatures, the combination of a number of measures offers comparatively greater added value. In this case, the construction effort is reduced by 5 percentage points when comparing variant 4B** to 6B**, i.e. after adding measure 6 to measures 1 and 2. As another maximum combined version, variant 6C** shows the possibility of achieving increased steam export with increased construction effort compared to variant 6B** with almost the same furnace efficiency. In this case, this is achieved by means of a serial connection of process steam superheating and feed preheating on the heat transfer medium side, i.e. the condensate formed in the process steam superheating is used downstream as a heat transfer medium for the feed preheating.

The examples listed in Table 2 use different designs of the air preheater sequences, with 2, 3 or 4 stages, with use of low-pressure steam and/or superheated (super-)high-pressure steam in addition to the explained use of feed water and/or (super-)high-pressure saturated steam.

The present invention can also be used in particular in a system such as that used in the EP 3 415 587 A1 and in which the cracked gas is cooled directly against the feed stream, so that only a portion of the heat released during the cracked gas cooling is used to generate (super) high-pressure steam. The application of the measures described in the present application also provides the same or at least almost the same advantages in such a system.

The present invention can also be used in a system with separation of carbon dioxide from the flue gas. In particular, when using measure 1 according to the invention, particularly low outlet temperatures of the flue gas are achieved at the end of the convection zone, which is advantageous for subsequent separation of carbon dioxide, e.g. by means of an amine scrubbing process (typical operating temperatures of amine scrubbing processes are 20 to 60°C).

In one embodiment of the invention, the combustion air can also be enriched with oxygen. No special purity requirements/concentration are necessary here; for example, the by-product of water electrolysis can be used, or any other technical source such as an air separation plant can be used. The effect of oxygen enrichment is approximately comparable to air preheating, since the adiabatic combustion temperature is increased in each case, resulting in increased radiation zone efficiency and a reduced amount of flue gas. The effect is not (quite) equivalent to air preheating, since the relatively higher oxygen content (with a lower nitrogen content, etc.) results in the equivalent effect with a slightly different flue gas composition. This is because proportionately more carbon dioxide and water are formed from combustion - the former is advantageous, for example, when carbon dioxide is recovered by means of amine scrubbing, and would apply even more so in the case of any flue gas recirculation. Another advantage is that radiation zone efficiency can be increased. or flue gas reduction and thus underfiring savings beyond the described values for air preheating with (super) high-pressure steam.

As already explained, the measures can be used for steam cracking furnaces with all possible hydrocarbon feedstocks. Examples include hydrocarbons with two, three and/or four carbon atoms (gaseous), naphtha (liquid), gas oil (liquid), and products from recycling processes such as plastics recycling (gaseous and liquid).

In all cases, all or only part of the combustion air can be preheated. Partial air preheating can be selected, for example, in the case where both bottom burners and side burners are used and only some of the burners are supplied with preheated air, preferably the bottom burners. The numerical values given for air preheating temperatures in this application always refer to the resulting preheating temperature of the entire combustion air. Process streams from other systems (e.g. gas turbine exhaust gas) can also be used to preheat the furnace air.

Variants 4 to 6 describe the heating of separate water or hydrocarbon streams against (super) high-pressure saturated steam. It can also be intended to heat a mixed stream of hydrocarbon and water in this way. This design is particularly relevant for use with gaseous inserts, since there is no change of unit of the insert in the convection zone.

The described application of saturated steam refers to the previously typical and technically used level of up to approx. 175 bar (abs.). Alternatively, it is also conceivable to provide partial saturated steam at a higher pressure and temperature level (e.g. 175 bar abs. and 355°C) for further preheating and/or superheating applications in the furnace area.

The present invention is preferably used in combination with the electric drive of individual or multiple compressors in the associated separating part of the system. This preferably compensates for the reduction in (super) high-pressure steam export from the furnaces caused by the air preheating according to the invention. Such increased electrification of the system also enables increased use of renewable energies by importing them from the power grid. The availability of steam boilers as backup systems for plant start-up is required to a lesser extent.

The measures described can be applied both to a completely new steam cracking furnace and to the modernization of existing furnaces. In the latter case, the advantages regarding the total bundle height are particularly relevant when, for example, it is a matter of accommodating modified bundle structures in an existing steel structure.

The invention is further explained below with reference to the figures, which illustrate embodiments of the present invention compared to the prior art.

Short description of the characters

The Figures 1 to 4 show arrangements not according to the invention.

The Figures 5 to 22 show arrangements according to embodiments of the invention and, where mentioned, arrangements not according to the invention.

Figure 23 summarizes embodiments of the invention and non-inventive embodiments in a schematic diagram.

In the above and the following further description, systems not according to the invention and designed according to embodiments of the invention and corresponding method steps based on these were and are described. For the sake of simplicity only, and to avoid unnecessary repetition, the same reference numerals and explanations were and are used for method steps and system components (for example a cooling step and a heat exchanger used for this purpose). In the figures, identical reference numerals are used for the same or comparable components and are also not explained again for the sake of clarity.

Detailed description of the figures

The advantages of the invention and corresponding embodiments are described below, particularly in comparison with the Figures 1 and 2 shown designs according to the state of the art (without air preheating and with central heating gas preheating according to Figure 1 and with air preheating to, for example, approx. 248°C according to Figure 2 , but central heating gas preheating as in Figure 1 illustrated). These considerations are based on a cracker furnace with naphtha as the feed. However, the different aspects of the invention apply equally to furnaces with gas or heavier liquid feeds.

The topology of the underlying convection zone 12 is particularly Figure 4 shown. However, other process arrangements can also be used within the scope of the invention. This topology comprises, counter to the direction of the outflowing flue gas Z, a first feed water preheater 121, a feed preheater 122, a second feed water preheater 123, a first high-temperature bundle 124, a process steam superheater 125, a first (super) high-pressure steam superheater 126, a second (super) high-pressure steam superheater 127 and a second high-temperature bundle 128.

Feed water W is passed through the first feed water preheater 121 and the second feed water preheater 123 and then fed to a corresponding (super) high pressure steam generation, for example in the cracked gas coolers 13. (Super) high pressure steam S generated there, which has not yet been superheated, is passed through the first (super) high pressure steam superheater 126 and the second (super) high pressure steam superheater 127 to obtain superheated (super) high pressure steam T, wherein feed water injection can take place between the first (super) high pressure steam superheater 126 and the second (super) high pressure steam superheater 127. Hydrocarbon feed H is heated in the feed preheater 122 and process steam P is heated in the process steam superheater 125 before both are combined to form the feed stream F and further heated in the first high temperature bundle 124 and the second high temperature bundle 128.

The explanations to the Figures 1 to 4 also apply to the following figures, as well as the figures in the Figures 1 to 4 used reference symbols are also used in the following figures. For the sake of clarity, not all material flows are referred to repeatedly in the following figures.

In the Figures 5 to 10 1A to 1F show variants of steam cracking systems according to a first group of embodiments according to the invention. The common feature of these is the use of cooled feed water for maximum energy recovery. The principle of all variants 1A to 1F shown is, as mentioned, to use the feed water already present at the furnace unit 10 as a heating medium for the air preheating 75 and optionally also for the heating gas preheating 65 in the low temperature range, i.e. in a temperature range of up to 100°C. The cooled feed water emerging from the preheating 75 and possibly 65 is then fed to the convection zone 12, but at a noticeably reduced temperature compared to the prior art, as also already mentioned.

The Figures 5 to 10 As mentioned, the preheaters shown can consist of several stages, e.g. a first stage with feed water as heating medium, a second stage with medium-pressure steam as heating medium and a third stage with (super) high-pressure steam as heating medium.

Other possible heating types or heating media can be used in addition, as mentioned. Furthermore, more or fewer preheating stages can be provided, as also mentioned. Please also refer to the above explanations for the use of draining heating medium or the return of condensate to the steam generation.

In the Figure 5 In the variant 1A illustrated, a portion of the feed water W is used as the corresponding heating current WH in the central air preheater 75. Another portion can be passed past the central air preheater 75 as a bypass WB in order to implement the control option explained. The latter is also the case in the variants 1B to 1F explained below.

In the Figure 6 In the variant 1B illustrated, parts of the feed water W are used as heating streams WH1, WH2 in the central air preheating 75 and the central heating gas preheating 65.

In the Figure 7 In the illustrated variant 1C, a decentralized air preheater 75 is heated with feed water WH, but no heating gas preheating takes place.

In the Figure 8 In the illustrated variant 1D, both a decentralized air preheater 75 with feed water WH1 and a decentralized heating gas preheater 65 with feed water WH2 are heated.

In the Figure 9 In the variant 1E illustrated, a decentralized air preheater 75 is heated with feed water WH1, but also a central heating gas preheater 65 is heated with feed water WH2. This results in two bypasses designated WB1, WB2.

In the Figure 10 In the illustrated variant 1F, a decentralized air preheater 75 is heated with feed water WH, whereas a centralized heating gas preheater 65 is carried out without heating with feed water.

In the Figures 11 to 13 2A to 2C are shown variants of steam cracking plants according to a second group of non-inventive embodiments. The feature that connects these is the use of the furnace's own (super) high-pressure saturated steam S as a heating medium in the air preheating 75. The principle of the variants shown is to use the saturated steam S generated in the steam generator 13 of the same cracker furnace 10 partly as a heating medium for heating 75 air in the medium to high temperature range, ie in a temperature range of 150 to 330°C. The steam supplied to the steam superheaters 126, 127 in the convection zone 12 (cf. Figure 4 ) is reduced accordingly, whereby proportionately more exhaust gas heat is available to the heat exchangers 121 to 125 arranged downstream in the path of the flue gas Z in the convection zone 12.

In the Figures 11 and 12 In the variants 2A and 2B illustrated, these measures are used together with a decentralized air preheating 75, whereby in the Figure 12 illustrated variant 2B additionally a central Air preheating, designated 75' for better differentiation, is present. In the Figure 13 In the illustrated variant 2C, however, there is only central air preheating. In all cases, a corresponding saturated steam flow used for heating is designated SH. Condensate formed from this is designated SC. In the illustrated examples, this is returned to the central steam system 50.

The resulting (super) high pressure condensate can be used as in the Figures 11 , 12 and 13 for variants 2A, 2B and 2C, are fed into the central steam system of the plant in order to further use the residual energy contained therein and finally to feed it to a suitable condensate treatment. It is also possible to reuse the condensate formed in whole or in part in previous preheating stages (ie at a lower temperature level), preferably after partial expansion to a reduced pressure level and addition of superheated steam at this reduced pressure level. However, subcooling of the condensate in the preheating can also be provided without prior expansion and addition of superheated steam.

In the Figures 14 and 15 3A and 3B show variants of steam cracking systems according to a third group of embodiments according to the invention. The feature that connects them is a combined use of feed water and (super) high-pressure saturated steam S as heating media in the air and/or heating gas preheating 65, 75. The principle of all variants shown is to apply the measures previously explained for the first and second groups of embodiments together, ie to use feed water W for the air and/or heating gas preheating 65, 75 in the low temperature range up to 100°C and additionally to use saturated steam for the air preheating 75 in the medium or high temperature range from 150 to 330°C.

As mentioned, the preheating can consist of several stages, e.g. a first stage with feed water as the heating medium, a second stage with medium pressure steam as the heating medium, and a third stage with super high pressure saturated steam as the heating medium. Other possible heating types or heating media can be used in addition, as mentioned. Furthermore, more or fewer preheating stages can be provided, as also mentioned. For the use of For the discharge of heating medium or the return of condensate to the steam generation, reference is also made to the above explanations.

In the Figure 14 In the variant 3A illustrated, these heating media are used together for a decentralized air preheating 75, whereas in the variant shown in Figure 15 In the variant 3B illustrated, there is also a central air preheater, again designated 75' for the sake of better differentiation, whereby the decentralized air preheater 75 uses (super) high-pressure saturated steam S and the central air preheater 76 uses feed water W.

In the Figures 16 and 17 variants of steam cracking plants according to a fourth group of embodiments are illustrated, designated 4A and 4B, wherein Figure 16 represents a non-inventive embodiment and Figure 17 an embodiment according to the invention. The feature that connects them is the use of (super) high-pressure saturated steam S as a heating medium for superheating process steam P. The principle of all variants shown is to use the saturated steam S generated in the steam generator 13 of the same furnace 10 partially as a heating medium for superheating process steam P in the medium to high temperature range, ie in the temperature range from 150 to 330°C. The steam superheaters 126, 127 for the saturated steam S in the convection zone 12 (cf. Figure 4 ) is reduced accordingly, whereby proportionately more exhaust gas heat at a higher temperature level is available to the heat exchangers 121 to 125 arranged downstream in the path of the flue gas Z in the convection zone 12. In addition, however, the load of the process steam superheater 125 in the convection zone 12 is also partially or completely reduced, so that even more exhaust gas heat at a higher temperature level is available to the heat exchangers 121 to 124 arranged downstream of the process steam superheater 125 in the path of the flue gas Z in the convection zone 12.

In the Figure 16 and 17 In the variants 4A and 4B illustrated, a decentralized process steam heating 35 is provided, whereby in the Figure 16 illustrated variant 4A only this one, in which in Figure 17 illustrated variant, a decentralized air preheater 75' is heated with (super) high-pressure saturated steam S as the heating medium. The Figure 17 illustrated variant also has, as an inventive embodiment, a use of feed water for Air preheating, in this case in an upstream central air preheating system 75.

In the Figures 18 and 19 variants of steam cracking plants previously designated 5A and 5B according to a fifth group of embodiments are illustrated, wherein Figure 18 represents a non-inventive embodiment and Figure 19 an embodiment according to the invention. The feature that connects them is the use of (super) high-pressure saturated steam S as a heating medium for preheating the hydrocarbon feed H. The principle of all variants shown is to use the saturated steam S generated in the steam generator 13 of the same cracking furnace 10 partly as a heating medium for preheating the hydrocarbon feed H (including possible partial evaporation in the case of liquid feeds) in the medium to high temperature range from 100 to 330°C. In this case, a single-phase preheating of the feed stream takes place on the feed side (liquid or gaseous). In addition, a partial or complete phase transition from liquid to gaseous can also take place (depending on the feed and outlet temperature). The steam superheaters 126, 127 for the saturated steam S in the convection zone 12 (cf. Figure 4 ) is reduced accordingly, whereby proportionately more exhaust heat at a higher temperature level is available to the heat exchangers 121 to 125 arranged downstream in the path of the flue gas Z in the convection zone 12. In addition, the load of the preheater 121 in the convection zone 12 is partially or completely reduced, so that even more exhaust heat at a higher temperature level is available to the heat exchanger 121 arranged downstream.

In the Figure 18 and 19 In the variants 5A and 5B illustrated, a decentralized insert heating 25 is provided, whereby in the Figure 18 illustrated variant 5A only this one, in which in Figure 19 illustrated variant, a decentralized air preheater 75' is heated with (super) high-pressure saturated steam S as the heating medium. The Figure 19 The variant illustrated also has, as an embodiment according to the invention, a use of feed water for air preheating, in this case in an upstream central air preheating system 75.

In the Figures 20 to 22 are variants of steam cracking plants previously designated 6A to 6C according to a sixth group of designs illustrated, where Figure 20 represents a non-inventive embodiment and Figures 21 and 22 inventive designs. The feature that connects them is a combined use of (super) high-pressure saturated steam S as a heating medium for process steam superheating and feed preheating. The principle of all variants shown is to use the saturated steam S generated in the steam generator 13 of the same cracking furnace 10 partly as a heating medium both for the superheating of process steam P in the medium to high temperature range from 150 to 330°C and for the preheating of the hydrocarbon feed stream H (including possible partial evaporation in the case of liquid feeds) in the medium to high temperature range from 100 to 330°C. The steam superheaters 126, 127 for the (super) high-pressure saturated steam S in the convection zone 12 (cf. Figure 4 ) is reduced accordingly, whereby proportionately more exhaust gas heat at a higher temperature level is available to the heat exchangers 121 to 125 arranged downstream in the path of the flue gas Z in the convection zone 12. In addition, the load of the superheater 125 for process steam P in the convection zone 12 is partially or completely reduced, so that even more exhaust gas heat at a higher temperature level is available to the heat exchangers 121 to 124 arranged downstream.

In the in the Figures 20 to 22 In the variants 6A to 6C illustrated, a decentralized feed heating 25 and a decentralized process steam superheating 35 are provided. In the variants shown in the Figures 20 and 21 In the variants 6A and 6B illustrated, these units are fed with saturated steam S in the manner shown. In the Figure 22 In the variant 6C illustrated, the process steam superheater 35 and the feed preheater 25 are connected in series on the heat transfer side. In the Figures 21 and 22 In the variants 6B and 6C shown, a decentralized air preheater 75' is additionally supplied with saturated steam S. The Figure 21 and 22 The variants illustrated in the drawings also comprise, as embodiments according to the invention, a use of feed water for air preheating, in this case in an upstream central air preheating system 75.

Figure 23 summarizes embodiments of the invention and non-inventive embodiments in a schematic diagram, whereby the corresponding material flows are not separately designated again. The Figure 23 illustrates in particular the possibility of central and decentralized provision of the previously explained units.

Claims (14)

1. Method for reacting one or more hydrocarbons by steam cracking, in which one or more input streams (F) containing the one or more hydrocarbons (H) are conducted, obtaining one or more product streams (C), through one or more radiation zones (11) of one or more cracker furnaces (10), in which the one or more radiation zones (11) are heated by firing heating gas (X) with combustion air (L), in which at least a portion of the combustion air (L) is subjected to combustion air preheating (75), in which steam (S, T) is produced from feed water (W), and in which the feed water (W) is subjected to feed water preheating in one or more convection zones (12) of the one or more cracker furnaces (10),
   characterized in that the combustion air preheating (75) is carried out at least in part and/or at least temporarily using heat withdrawn from at least a portion of the feed water (W) upstream of the feed water preheating.
2. Method according to claim 1, wherein the steam generated from the feed water (W) comprises superheated and/or non-superheated high-pressure or super-high-pressure steam (T) formed from the feed water (W) after the feed water preheating.
3. Method according to claim 2, wherein at least a portion of the feed water (W) is subjected to feed water evaporation after the feed water preheating using heat withdrawn from at least a portion of the one or more product streams (C), obtaining high-pressure or super-high-pressure steam (S).
4. Method according to claim 3, wherein at least a portion of the high-pressure or super-high-pressure steam (S) is subjected to steam superheating in one or more convection zones (12) to obtain superheated high-pressure or super-high-pressure steam (T).
5. Method according to any of claims 2 to 4, wherein the combustion air preheating (75) is further performed using heat withdrawn from a portion of the superheated high-pressure or super-high-pressure steam (T).
6. Method according to any of the preceding claims, wherein the heating gas (X) is subjected to heating gas preheating (65) which is likewise carried out using heat which is withdrawn from at least a portion of the feed water (W) upstream of the feed water preheating.
7. Method according to any of the preceding claims, wherein the feed water preheating is performed in one or more flue gas channels in the one or more convection zones (12), the feed water preheating being performed at a lower temperature level than for steam superheating, to obtain the superheated high-pressure or super-high-pressure steam (T), and for a process steam superheating to provide sufficiently heated process steam which is used to form the one or more input streams (F).
8. Method according to any of the preceding claims, wherein the feed water (W) is provided at a temperature level of 80 to 140 °C and wherein the feed water (W) is cooled to a temperature level of 40 to 100 °C at the combustion air preheating (75).
9. Method according to any of the preceding claims, wherein the feed water (W) is supplied to the combustion air preheating (75) at a pressure level of 30 to 60 bar absolute pressure or 60 to 175 bar absolute pressure and is subjected to the feed water preheating at this pressure level.
10. Method according to any of claims 1 to 8, wherein the feed water (W) is supplied to the combustion air preheating (75) at a pressure level of 20 to 60 bar absolute pressure and is subjected to the feed water preheating at a pressure level of 30 to 60 bar absolute pressure or 60 to 175 bar absolute pressure.
11. Method according to any of the preceding claims, wherein multiple cracker furnaces (10) are used which are supplied with the feed water (W) by means of a central feed water system (40), the combustion air preheating (75) being carried out separately for each of the multiple cracker furnaces (10) or together for the multiple cracker furnaces (10).
12. Method according to any of the preceding claims, wherein the air preheating is further carried out using saturated steam and/or steam condensate formed therefrom.
13. Method according to any of the preceding claims, wherein a preheating of the one or more input streams (F) and/or one or more substance streams used for the formation thereof is carried out using saturated steam and/or steam condensate formed therefrom.
14. System for reacting one or more hydrocarbons by steam cracking, which comprises one or more cracker furnaces (10) having one or more radiation zones (11) and which is designed to guide one or more input streams (F), containing the one or more hydrocarbons (H), through the one or more radiation zones (11) of the one or more cracker furnaces (10), obtaining one or more product streams (C), the system comprising one or more burners for heating the one or more radiation zones (11) by firing heating gas (X) with combustion air (L), the system having combustion air preheating (75) and being designed to heat at least a portion of the combustion air (L) in the combustion air preheating (75), the system having one or more steam generators which is/are designed to generate steam (S, T) from feed water (W), and the system being designed to subject the feed water (W) in one or more convection zones (12) of the one or more cracker furnaces (10) to feed water preheating, characterized in that the combustion air preheating (75) comprises heat transfer means which are designed to at least temporarily transmit heat, which is withdrawn from at least a portion of the feed water (W) upstream of the feed water preheating, to the combustion air.

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