BR102014000540A2 - method for designing the construction of a heat exchange reformer (her) - Google Patents

Abstract

method for designing the construction of a heat exchange reformer (her). The present invention relates to a method for designing the construction of a heat exchange reformer (her) to minimize metal dust formation, and a method for improved thermal control in a heat exchange reformer (her). ). By analyzing the various parameters related to a main reform unit (mru) and a heat exchange reformer (her), improved thermal control and reduced metal dust formation are obtained.

Description

Patent Descriptive Report for "METHOD FOR DESIGNING THE CONSTRUCTION OF A HEAT EXCHANGE (HER) REFORMER".

With respect to the production of a synthesis gas by steam reforming, high temperatures are required in order to obtain a reliable conversion of hydrocarbons into synthesis gas.

In traditional synthesis gas plants, sensitive heat in the synthesis gas is used for steam generation. Performing an analysis of the crush points in this regard will typically lead to the conclusion that the sensitive heat in the reformer gas may be better utilized, as the temperature difference in the hot tip is in the range of 650 to 75013. However, due to the corrosion phenomenon known as metal dust formation, it is a challenge to design the heat exchanger in such a way that the reliability of the plant is not compromised. Even in waste heat boilers used in traditional synthesis gas factories where the likelihood of metal dust affinity hot metal surfaces is significantly reduced due to the relatively low temperature and high heat transfer coefficients in the steam / water side, failures due to metal dust formation have been observed.

When designing an apparatus that uses the sensitive heat of the steam reforming section, it is therefore of the utmost importance that significant knowledge and experience of the phenomenon of metal dust formation is available.

Typically, crush point analysis and / or CAPEX / OPEX assessments show that the temperature approach must be between 10 and 15013 to achieve an optimal balance between investment and operating cost. A higher value is generally relevant for more "exotic" materials, ie in environments with high temperature and / or high corrosion potential.

For the generation of a synthesis gas, the temperature output in the main reforming section is in the range 850 to 105013, which means that sensitive heat can be used to heat a process flow to 600 to 900Ό. Such a flow does not exist in the synthesis gas process beyond the reform process itself. Accordingly, different concepts have been considered in using sensitive heat in a main reformer's synthesis gas for further steam reforming, for example, see Aasberg-Petersen K., Dybkjaer I., Ovesen CV, Schjodt NC, Sehested J ., Thomsen SG "Natural gas to synthesis gas - Catalysts and catalytic processes", Journal of Natural Gas Science and Engineering, 2011. The gas-heated steam reformer may be located or in series with the main reformer (referred to as HTER-s, ie. heat exchanger reformer) or in parallel (HTER-p) with the main reformer. The primary reformer may be a tubular reformer, a secondary reformer or a self-thermal reformer. The HTER-s reformer has the advantage that a higher average outlet temperature can be obtained, which is advantageous over the total feed conversion and also - in particular to a synthesis gas to a synthetic fuel - a higher CO ratio. / H2, while the total pressure drop at the front end is smaller for the HTER-p reformer concept. In the following, only the HTER-p reformer will be described, and Figures 1 to 3 show the implementation of the HTER-p reformer in different types of factories.

Typical main reformer operating parameters are shown in Table 1. The HTER-p reformer rate may typically be up to 40-50% with respect to the Waste Heat Boiler (and steam supercharger, if applicable) function. ) applied in a standard factory setting, and the retrofit capacity corresponds to 25 - 30% of the capacity of the main reformer. In ammonia, methanol and hydrogen factories, this means that the tubular / primary reformer rate can be reduced accordingly. In addition to the reduction in reformer size, fuel consumption and waste heat to be recovered are also significantly reduced, resulting in lower total fuel + fuel consumption and reduced size of reformer waste heat section. tubular. In factories where the autothermal reformer (ATR) is applied, the oxygen requirement for the ATR reformer is reduced, resulting in a lower operating cost for the air separation unit and a smaller unit. Since economies of scale are, in particular, relevant to synthetic fuel factories, and since the capacity of the air separation unit is often a bottleneck, the implementation of the HTER-p reformer (and the HTER reformer) -s) can boost the total factory capacity to the same consumption of O2.

As described above, feed efficiency and fuel efficiency of the synthesis gas plant are improved, and CO2 emission is reduced. In some cases, however, steam generated at the synthesis gas plant may have important value in the complex as a whole, and in such cases it is important to value the export of steam from the synthesis gas plant; see Andersen NU, Olsson HL, "The Hydrogen Generation Game", Hydrocarbon Engineering 2011. Often the efficiency of steam generation in the synthesis gas plant can be as high as 94%, while the typical efficiency of an auxiliary boiler is 92.5%. However, as the efficiency of the auxiliary boilers increases (eg by implementing low-calorie power generation through the use of the Rankine Organic Cycle) and a main pump and compressor units switch to electricity, the advantage of the HTER reformer becomes increasingly significant.

In the HTER-p reformer, high heat transfer coefficients are obtained compared to the total heat transfer obtained in burnt tubular reformers and this results in a very small ground area for the HTER-p reformer compared to the tubular reformer ( see Table 2). It is noted that the heat intensity for the HTER-p reformer is greater than a factor 10 greater than the intensity for a typical tubular reformer, which supports the fact that an HTER-p reformer is a workable way to add a capacity. renovation to a new or existing tubular reformer, despite the fact that the construction of the HTER-p reformer is more complicated and the construction materials are more expensive. In order to minimize the total cost of an entire plant, it is important to know the crucial parameters in the plant as a whole. Topsoe has two types of HTER-p reformer in commercial operation: 1) the bayonet tube HTER-p reformer, and 2) the two-tube HTER-p reformer. The HTER-p bayonet tube reformer (see Figure 4) consists of a tube bundle in which each tube assembly consists of three concentric tubes. In the outer annular crown flow, the main reformer heating gas flows upward, in the intermediate annular crown the feed gas flows downward through a catalyst bed from which it exits and turns into the central tube. (the bayonet tube) and flows upward into the outlet chamber, where the cooled retread gas is mixed with the cooled annular crown cooler heating gas. The two-tube HTER-p reformer (see Figure 5) consists of a dual-tube bundle of tubes. The catalyst is charged into the center pipes and out of the outer pipes. Feed gas flows downward through the tube inside the catalyst and through the tube outside the catalyst. Reformed gas from the catalyst beds is mixed with the main reformer heating gas and upstream fluid in the annular crown between the twin tube assembly, while exchanging heat with the gas flowing in the catalyst beds.

Typically, in factories where high conversion is very important, the temperature output in the catalyst bed will be as high as possible to ensure minimal leakage of methane into the synthesis gas. This is, for example, often the case in ammonia plants and hydrogen plants with a tight fuel balance when operating at a low vapor to carbon ratio. In such a case, the HTER-p bayonet type reformer is ideal as the heating gas of the main reformer (tubular reformer or secondary reformer) is not mixed with the effluent gas catalyst reformer of the HTER-p reformer before Heat exchange happens. This results in a higher reform temperature (approximately 30 to 400 ° C) on the HTER-p reformer for the same approach to the hot end temperature of the HTER-p reformer than for the two-tube HTER-p reformer. In cases where methane leakage is less significant, the two-tube HTER-p reformer has the advantage of being more compact as the space between tube assemblies is used as a catalyst bed and makes the HTER-p reformer p even more compact. The two-tube HTER-p reformer is typically the most feasible solution in ATR reformer-based plants where the main reformer outlet temperature is relatively high, and in hydrogen plants where fuel balance allows this design (often in factories where the vapor to carbon ratio is determined by the type of raw material).

The above criteria are only typical, and many other factors may influence the final and more feasible layout of the HTER-p reformer.

A major challenge with heat exchange reformers heated by the reformed process gas is corrosion from metal dust formation, which typically can occur in a temperature range of 400 to 800 * 0 in CO and / or hydrocarbons. The precursor to metal dust formation is carbon formation and the possible mechanisms for carbon formation in a reformed gas are, see Agüero A ,, Gutiérrez M., Korcakova L., Nguyen TTM, Hinnemann B. ,, Saadi S .. "Metal Dusting Protective Coatings. A Literature Review", Oxidation of Metals, 2011: Boudouard Reaction CO Reduction Methane Decomposition Both Boudouard Reaction (1) and CO Reduction Reaction (2) they are exothermic reactions, that is, when the current temperature is below the equilibrium temperature, there is an affinity for carbon formation from both reactions. However, at a certain temperature, for example 400 to 450C, the reaction rate is so low that negligible corrosion in practice will occur. The methane decomposition reaction (3) is endothermic, ie the affinity for carbon formation exists above equilibrium temperature. Table 3 shows typical equilibrium temperatures for the carbon formation reaction.

The process gas is observed to pass through the critical temperature range, and the affinity for carbon formation and the potential for metal dust formation exist. Achieving an affinity for carbon is not necessarily equal to obtaining an unacceptable corrosion of metal dust formation (but this is often the case). Some commercial alloys have long incubation times and low corrosion rates, making them suitable for operation under conditions with affinity for metal dust formation. However, operation under affinity conditions for carbon formation requires extensive analysis prior to use in commercial units, and Topsoe is continually analyzing materials and operating conditions to map the metal dust formation attacks in the laboratory. and has an extensive collaboration of leading companies that develop special alloys. Last but not least, Topsoe has in fact had successful industrial experience for over a decade in the operation of convective reformers in the field of metal dust formation. Haldor Topsoe A / S (Topsoe) has had convective reformers in operation since 1990. The first heat exchanger reformers were based on convection from combustible gases (Haldor Topsoe Convective Reformers, "HTCR"). Most HTCR reformers in operation (over 30) are bayonet-type (see Figure 6) and actually have complex heat transfer mechanisms. Extensive fe-edback and heat transfer experience in convective reformers has been gained from these appliances and has been used to optimize the design of other types of convective reformers.

In 2003, the first HTER reformer was successfully introduced in South Africa at Sasol's Secunda Synthetic Fuel Plant and has been in operation ever since (Thomsen SG, Han PA, Loock S., Ernst W. "The first Industrial Experience with the Haldor Topsoe Exchanger Reformer ", AlChE Ammonia Safety Symposium, 2006). The HTER reformer is a two-tube type and when applying the HTER reformer, synthesis gas production was increased by over 30%. The operating conditions for this reformer are relatively critical with respect to metal dust formation due to the high temperature and low vapor to carbon ratio. The first tube bundle was in operation for over seven years and the metal dust corrosion was within the expected rate and provided no reason for tube bundle replacement.

In 2010, a bayonet-type HTER reformer was started in India at Numaligarh Refinery Limited (Konwar S., Thakuria A .. "New Paradigms in Revamp Options for Hydrogen Units - The HTERp in NRL", 16th Refinery Technology Meet., 2011 ). The HTER reformer was part of a refurbishment of a general refinery H2 demand, complex due to stricter environmental regulations for fuel products. The existing capacity of the existing Hydrogen Unit was 38000 MTPY (52,400 Nm3 / h) and the additional H2 output provided by the HTER reformer was 14,600 Nm3 / h, ie a capacity increase of over 25%.

In 2007, the companies Essar Oil Vadinar Limited and Haldor Topsoe agreed to design a hydrogen unit with a capacity of 130,000 Nm3 / h of hydrogen.

Considering the operating cost and power and fuel efficiency advantages of the hydrogen unit, Essar Oil decided to implement a two-tube HTER reformer. The hydrogen unit configuration is shown in Figure 7. The plant is designed for high flexibility with natural gas, refinery flue gas, LPG gas and naphtha as raw materials. In order to accommodate the high flexibility in the raw materials, a vapor-to-carbon ratio of 2.5 has been selected for the pre-reformer and tubular reformer, ensuring optimal pre-reformer operation. The tubular reformer has been designed with a maximum operating output temperature of 9150 for the highest efficiency and conversion, and furthermore allows for even better use of the HTER-p reformer. The HTER-p reformer rate is approximately 23 Gcal / h, which corresponds to approximately 40% of the sensitive heat in the synthesis gas when it cools to approximately 2800 (the normal outlet temperature from the Refuse). The rate also corresponds to a reduction in power and fuel to the hydrogen unit of approximately 5% (and steam exports are reduced accordingly).

As mentioned above, it is very important to ensure that the temperature of metal surfaces is within certain limits in order to avoid excess corrosion caused by metal dust formation. For the HTER-p reformer of the Essar H2 and Oil plant, the most important parameter is the CO reduction temperature. When synthesis gas passes the critical temperature with affinity for metal dust formation while transferring heat to the catalyst beds, it is important that materials with sufficient metal dust resistance are selected for the relevant parts of the beam. of pipes. Material selection is optimized by considering both cost and operational flexibility. Since the Essar H2 and Oil plant is designed with a pre-reformer, and the feed for the HTER-p reformer is downstream of the pre-reformer, the feed composition (at a constant vapor to carbon ratio). ) for the HTER-p reformer becomes relatively constant, regardless of the change in raw material type (NG, RFG gasoline, LPG gas, or naphtha), but other parameters are important for the temperature profile in the HTER reformer: - Ratio relative power supply for HTER reformer compared to tubular reformer - Tubular reformer output temperature - Vapor to carbon ratio Figure 8 shows the impact of the above parameters on the temperature profile. Material selection is designed to ensure a robust design that allows for variations in factory operating parameters, and in order to facilitate control and minimize corrosion caused by metal dust formation, the factory is designed with algorithms that ensure that the power flow to the HTER reformer is controlled optimally.

As seen in Figure 8, significant parameters for the temperature profile are the HTER reformer feed flow rate and the tubular reformer outlet temperature. Since the outlet temperature of the tube reformer can be determined by other criteria (the metal temperature of the tube reformer, the tube burn rate, etc.), it has been selected to handle the feed flow rate for the flow. HTER reformer to provide an ideal temperature profile on the HTER reformer: FhTER - f (Ftub.refj T0ut, tub.refj S / C) where Fhter is the feed rate for the HTER reformer Ftub.ref is the feed flow rate for the tubular reformer Tout.tub.ref is the outlet temperature of the tubular reformer S / C is the vapor-to-carbon ratio for the reforming section. ) means the molar ratio of H20 to carbon in a given process flow.

Equilibrium temperatures for carbon formation reactions are affected by the outlet temperature of the tubular reformer and the vapor to carbon ratio. Equilibrium temperatures are reduced to a lower outlet temperature and a higher vapor to carbon ratio, so that the operating conditions considered milder for the tubular reformer are also milder for the HTER reformer and thus offer a kind of self-regulating. as long as the power ratio for the HTER reformer and the tubular reformer remains constant. However, it is always recommended to use advanced algorithms as this will facilitate control and minimize the risk of premature failure due to malfunction. The HTER-p reformer was designed and obtained by the Topsoe company. The pressure capsule is of a refractory lining, and the refractory was dried on site in August 2011 prior to commissioning of the factory. The pressure capsule refractory may not be dried during pre-commissioning / commissioning (such as the refractory in the outlet manifold) as no flow is intended to pass through the refractory during commissioning (or operation).

In September 2011, the pressure capsule was erected and the tube bundle was installed. The HTER-p reformer was loaded with Topsoe's catalyst for 16x8 mm heat exchange reformers in November 2011, and passed smoothly and with a very small deviation between load densities and pressure drops (+3.1 /-2.2%) on the obtained tubes. This ensures a good flow distribution between the pipes. The total catalyst loading time for both in-pipe and out-of-pipe catalyst was ten days in daily shifts. This time is expected to be reduced and compared to a conventional tubular reformer with a similar H2 production capacity (-32,000 Nm3 / h, corresponding to 80 to 100 reformer tubes), the loading time for the HTER reformer it was only 3-4 days longer, which may be considered reasonable given the compactness of the HTER reformer and the fact that the load of the HTER reformer is typically not on a critical path. The H2 plant was mechanically completed and fully pre-commissioned in January 2012 and commissioning was started immediately thereafter. Heating of the reform section (the pre-reformer, tubular reformer and HTER-p reformer) in circulating nitrogen was started on January 12, and on January 15 the feed was introduced into the reform section. The Essar H2 and Oil plant is designed with an Average Temperature Deviation (MTS), and due to the availability of import hydrogen for starter, it was decided to reduce the MTS diversion catalyst through the H2 produced by the plant itself. H2 with Average Temperature Deviation exceeded. This can be done by operating the reforming section at a reduced capacity, at the reformers' reduced outlet temperatures (the tubular reformer and the HTER reformer), and at a higher vapor-to-carbon ratio, thereby producing a synthesis gas from suitable for supply to the Pressure Oscillation Adsorption (PSA) unit and thereby producing H2 for the catalytic reduction of the MTS offset. The catalytic reduction of the MTS offset was completed on January 20, and the Average Temperature Converter was inserted on the same day, and on January 21, 2012 a capacity of 60% was reached, and on January 22, 2012 a capacity of 85% production was achieved. The H2 plant was operated according to each H2 demand in the refinery complex. The H2 plant was restarted early in the second quarter of 2012, and in May 2012 a 100% capacity demonstration was performed. Operational data has been analyzed using a data reconciliation program that ensures that the HTER plant and reformer analysis is based on a consistent data set without errors on heat and mass balances. Operating and consumption amounts were as expected at a production capacity of 130,130 Nm3 / h, and it was shown through on-site optimization that better than expected and guaranteed consumption amounts could be obtained (see Table 4). . The operation and performance of the HTER-p reformer during the demonstration performed was also evaluated, and the measured temperatures fit well with the temperatures simulated by Topsoe's reformer model (see Figure 9), and indicate that the current heat transfer at the beginning execution is slightly better than the heat transfer predicted by the model.

An assessment of the temperature profile when comparing the direct output of the reformer model with a simulation using reconciled terminal temperatures indicates that the critical temperature position shifts only approximately 0.5 m, and for this case (and generally for HTER-p two-tube reformer) the position moves upwards, that is, even further for the part of the tube assembly consisting of materials with high resistance to metal dust formation. See, for example, Figure 10.

In short, installing a Haldor Topsoe Exchange Reformer can significantly reduce power and fuel consumption for an H2 plant and thus also the CO2 emission from the factory. The HTER-p reformer is a very compact reformer with very high heat intensity, which makes it achievable for both base factories as well as for renovation projects. It is important that design tools for reformer sizing come from both heat transfer and catalytic activity precisely and take into account the interaction between thermal design and catalytic performance. Overestimation of heat transfer and catalytic activity will result in a device that will not be able to meet design capability, but applying a "design margin" is not the solution as too much heat transfer High catalyst activity and / or very high catalytic activity may result in critical operation with metal dust formation attacks. Commissioning and operation of the Essar H2 and Oil plant shows that the implementation of the HTER-p reformer does not adversely affect commissioning and startup time, and the operation of the HTER-p reformer is robust and safe and does not affect the reliability of the factory. The evaluation of Essar's H2 and Oil plant operating data shows that the models used for predicting heat transfer and catalyst are very accurate and guarantee the proper and safe design of the HTER-p reformer. Nine units with the Topsoe-designed HTER-p reformer are expected to be started from 2013 to 2015. United States Patent No. 6224789 describes a process for the production of a synthesis gas comprising an autothermal reformer and a reformer. parallel heat exchange in which the autothermal reformer effluent is used to heat the heat exchange reformer.

By the present invention there is provided a method in which a metal dust resistant metal is used at a distance from the input of the heat exchanger reformer, and in which such distance is calculated from the vapor to heat ratio. carbon, the effluent outlet temperature and hydrocarbon flow of the main reformer, as well as the vapor-to-carbon ratio and hydrocarbon flow rate of the heat exchanger.

According to and in accordance with the appended claims, the aspects of the present invention are as follows: Aspect 1. A method for designing the construction of a Heat Exchange Reformer (HER) to minimize the formation of metal dust, said reformer HER being part of a synthesis gas production unit, said synthesis gas production unit comprising a Main Reform Unit (MRU) and a Heat Exchange Reformer (HER), in which the effluent from the The MRU unit is arranged to provide heat to the HER reformer, and in which a hydrocarbon feedstock is arranged to pass in parallel through both the MRU unit and the HER reformer, thereby providing: MRU unit hydrocarbon having a MRU unit vapor to carbon ratio (MRUS / c), an effluent outlet temperature (TMru) and an MRU unit hydrocarbon flow rate (Fmru) 6 b) a HER reformer having a vapor to carbon ratio in the HER reformer (HERS / c) and a HER reformer hydrocarbon flow rate (FHer), - said method comprising the steps of: - determining how the temperature profile within the HER reformer varies with the distance from the HER reformer inlet as a function of the ratio of FHer / Fmru flow rates, the MRU unit outlet temperature (TMru), the MRU unit vapor to carbon ratio (MRUs / c) , the vapor to carbon ratio in the HER reformer (HERS / c) and the total hydrocarbon flow rate (FMRU + FHer); - from said temperature profile, determine a distance (A) from the HER reformer inlet at which metal dust formation is not significant; - at a distance greater than said distance (A) from the entrance of the HER reformer, construct the HER reformer from a first metal with a greater resistance to metal dust formation; and - at a distance less than said distance (A) from the entrance of the HER reformer, to construct the HER reformer from a second metal having a lower resistance to metal dust formation than said first metal.

Aspect 2. A method for improved thermal control in a Heat Exchange Reformer (HER) of a synthesis gas production unit, said synthesis gas production unit comprising a Main Reform Unit (MRU) and a Heat Exchange Reformer (HER), in which the effluent from the MRU unit is arranged to provide heat to the HER reformer, and in which a hydrocarbon feedstock is arranged to pass in parallel through both the MRU unit. HER reformer, thus providing: a) a hydrocarbon feed from the MRU unit having a vapor to carbon ratio of the MRU unit (MRUS / c), an effluent outlet temperature (TMru) and a hydrocarbon flow rate from the MRU (Fmru) unit (b) a HER reformer hydrocarbon feed having a HER reformer hydrocarbon flow rate (FHer), - said method comprising: adjusting the Fher / Fmru rate ratio by adjusting the flow rates of the HER reformer. for the MRU unit and HER reformer based on the MRUs / c ratio, the Tmru temperature, the HERS / c ratio, and the total hydrocarbon flow (FMru + FHer) to maintain a stable temperature profile in the Heat Exchange Reformer (HER).

Aspect 3. The method according to aspect 2, wherein the method comprises increasing or decreasing the Fher / Fmru flow rate ratio, preferably decreasing the Fher / Fmru- flow rate ratio. method according to aspect 2, wherein the method comprises increasing or decreasing the MRU unit vapor-to-carbon ratio (MRUs / c), increasing or decreasing the effluent outlet temperature of the MRU unit (TMru), increasing or decreasing the vapor to carbon ratio in the HER reformer (HERS / c) and / or increasing or decreasing the total hydrocarbon flow (FMru + FHer).

Aspect 5. The method according to aspect 4, wherein the method comprises increasing the vapor to carbon ratio of the TR reformer (TRs / c).

Aspect 6. The method according to any of the preceding aspects, wherein the HER reformer is a bayonet-type HER reformer or a two-tube HER reformer.

Aspect 7. A method according to any of the preceding aspects, wherein said method comprises decreasing the flow rate ratio Fher / Fmru- Aspect 8. A method according to any of the preceding aspects, wherein the unit MRU provides a synthesis gas for a hydrogen plant, an ammonia plant, a methanol plant and / or a synthetic fuel plant.

Aspect 9. A method according to any of the preceding aspects, wherein the MSR reactor is selected from a tubular reformer, an air blown secondary reformer, an oxygen blown secondary reformer and an autothermal reformer.

Aspect 10. A method according to any of the foregoing aspects, wherein the effluent from the MRU unit is arranged to flow upstream or downstream with the HER reformer hydrocarbon feed into the HER reformer.

Aspect 11. A method according to any of the preceding aspects, wherein the hydrocarbon feedstock comprises natural gas, LPG gas, naphtha, reformulated gasoline (RFG) or a mixture of LPG gas and naphtha.

Aspect 12. A method according to any of the preceding aspects, wherein said synthesis gas production unit further includes a pre-reformer disposed upstream of the MRU unit and / or the HER reformer.

Aspect 13. Use of a method according to any of aspects 2 to 11 for reduced metal dust formation in the HER reformer.

Claims (13)

1. Method for designing the construction of a Heat Exchange Reformer (HER) to minimize metal dust formation, said HER reformer being part of a synthesis gas production unit, said synthesis gas production unit. comprising a Main Reform Unit (MRU) and a Heat Exchange Reformer (HER), wherein the MRU effluent is disposed to provide heat to the HER, and wherein a hydrocarbon feedstock is disposed of running in parallel through both the MRU and HER units, thus providing: a. an MRU hydrocarbon feedstock having an MRU vapor to carbon ratio (MRUs / c), an effluent outlet temperature (Tmru) and an MRU hydrocarbon flow rate (FMru) and b. a hydrocarbon feedstock in HER having a vapor to carbon ratio in HER (HERS / c) and a hydrocarbon flow rate of HER (Fher), - the method comprising the steps of; - determine how the temperature profile within the HER varies with the distance from the HER inlet as a function of the Fher / Fmru ratio, the MRU outlet temperature (Tmru), the MRU vapor to carbon ratio (MRUs / c) the vapor to carbon ratio in the HER (HERS / c) and the total hydrocarbon flow rate (FMru + FHer); - from said temperature profile, determine a distance (A) from the inlet of the HER at which metal dust formation is not significant; - at a distance greater than said distance (A) from the inlet of the HER, construct the HER of a first metal with a higher resistance to metal dust formation; and - at a distance less than said distance (A) from the inlet of the HER, construct the HER of a second metal that has a lower resistance to metal dust formation than said first metal. Method for improved thermal control in a Heat Exchange Reformer (HER) of a synthesis gas production unit, said synthesis gas production unit comprising a Main Reform Unit (MRU) and a Heat Exchange (HER), wherein the effluent from the MRU unit is arranged to provide heat to the HER, and where a hydrocarbon feedstock is arranged to pass in parallel through both the MRU and HER, thus providing: a. an MRU hydrocarbon feedstock having an MRU vapor to carbon ratio (MRUs / c), an effluent outlet temperature (TMRU) and an MRU hydrocarbon flow rate (FMru), and b. HER hydrocarbon feed having a HER reformer hydrocarbon flow rate (FHer), - the method comprising the step of: adjusting the FHer / Fmru ratio by adjusting the hydrocarbon flows to the MRU and HER based on MRUs / c, TMru, HERS / c, and total hydrocarbon flow (FMru + FHer) to maintain a stable temperature profile in the Heat Exchange Reformer (HER) . Method according to Claim 2, characterized in that the method comprises increasing or decreasing the Fher / Fmru ratio, preferably decreasing the Fher / Fmru ratio. Method according to claim 2, characterized in that the method comprises increasing or decreasing the MRU vapor-to-carbon ratio (MRUs / c), increasing or decreasing the effluent outlet temperature of the MRU. (Tmru), the increase or decrease of the vapor to carbon ratio in HER (HERS / C) and / or the increase or decrease of the total hydrocarbon flow (FMru + FHer). Method according to claim 4, characterized in that the method comprises increasing the vapor to carbon ratio of the TR reformer (TRS / c). Method according to any of the preceding claims, characterized in that the HER is a bayonet-type HER or a two-tube HER Method according to any one of the preceding claims, characterized in that said method comprises decreasing the FHer / Fmru · ratio. Method according to any one of the preceding claims, characterized in that MRU provides a synthesis gas for a hydrogen plant, an ammonia plant, a methanol plant and / or a synthetic fuel plant, Method according to any one of the preceding claims, characterized in that the MSR is selected from a tubular reformer, an air blown secondary reformer, an oxygen blown secondary reformer and an autothermal reformer. Method according to any one of the preceding claims, characterized in that the effluent from the MRU is arranged to flow upstream or downstream with the HER hydrocarbon feed into the HER. Method according to any one of the preceding claims, characterized in that the hydrocarbon feedstock comprises natural gas, LPG gas, naphtha, reformulated gasoline (RFG) or a mixture of LPG gas and naphtha. Method according to any one of the preceding claims, characterized in that said synthesis gas production unit further includes a pre-reformer disposed upstream of the MRU and / or HER. Use of a method as defined in any one of claims 2 to 11, characterized in that it is intended to reduce the formation of metal dust in the HER.