BACKGROUND OF THE INVENTION

The invention relates to a syngas cooling assembly and method.

Syngas is a commonly used abbreviation of the term synthetic gas and generally comprises a mixture of, at least, Hydrogen (¾) and Carbon Monoxide (CO) . Syngas may be

produced by partially oxidizing coal, heavy petroleum

residues, biomass and/or another carbonaceous feedstock at a high temperature in a gasification reactor.

When leaving the gasification reactor the syngas may have a temperature between 1300 and 1600°C.

The syngas may subsequently be quenched to temperatures between 700 to 1000°C and then further cooled down to a temperature typically below 350°C in a Syn-Gas Cooler (SGC) which comprises a Steam Super Heater and several water evaporator heat exchangers .

Such Syn-Gas Coolers (SGCs) , or syngas cooling

assemblies, are known from, for instance, international patent applications WO2011/089140, WO2011/003889,

WO2012/028550 and WO2013/041543.

The known Syn-Gas Coolers (SGCs) comprise a Steam Super Heater heat exchanger, also known as SSH, and one or more heat exchangers in which water is evaporated (¾0-Evap) , which are known as evaporators, are positioned downstream of the Steam Super Heater (SSH) heat exchanger when seen in the flow direction of the syngas.

In the conventional Syngas Cooler (SGC) designs known from these prior art references the superheater (SSH) is placed directly at the inlet of the SGC, when seen in the syngas flow direction. In most of the conventional coal and other carbonaceuous feed gasification plants the SSH is underperforming, a.o. because of a flow maldistribution and fouling at the inlet of the SGC.

The Steam Super Heater (SSH) is generally fed by

saturated steam. The saturation temperature depends on the drum pressure level and is typically around 275°C. The saturated steam is superheated in the SSH up to certain temperature which is typically about 400°C. The high pressure high temperature steam could be used for different

applications such as steam turbine power generation and/or process applications.

In some applications there could be another set of heat exchangers installed downstream the evaporators which are called economizers. An economizer has a similar heating surface configuration as other heat exchangers but it is fed by subcooled water. The feed water, which is coming from high pressure pumps, is preheated in the economizer and then it is fed to a cooling water and steam supply and re-circulation drum via which cooling water and saturated is supplied to the SSH and other heat exchangers. By installing the economizer the thermal efficiency may be increased substantially.

However, because of the high acid dew point in the syngas installing the economizer in the SynGas Cooler (SGC) may not be feasible.

Therefore, in most of the conventional SGCs, the feed water is fed directly to the cooling water and steam supply and re-circulation drum. In general, depending on the

gasification plant configuration, the SGC and drum could have more than one water/steam pressure level. In such case the SGC and drum designs and heating surface arrangements are substantially similar to those for a single pressure level arrangement. As more than one water/steam pressure level is not quite common in the Coal Gasification business reference will be made in this specification to only a single pressure level arrangement.

The superheated steam discharged by the SSH may be supplied to a steam turbine to generate electric power. In such case the mass flow rate, pressure and temperature of the superheated steam leaving the Super Heater (SSH) needs to be predictable and guaranteed by the designer. This guarantee is, most of the time, a part of the contract obligations and subject to liquidate damage which depends on the shortfall in steam mass flow rate and temperature. A principal reason for this shortfall is that the steam power output drops down by decreasing the steam mass flow and temperature. If the steam temperature drops down below certain level then the steam turbine has to bypassed and therefore, it will be tripped. It means that the reliability of the steam turbine depends on the SSH performance, so that unexpected SSH underperformance may cause significant operational losses. For the existing syngas cooling assemblies, the most difficult challenge is to reach a predetermined steam temperature at SSH outlet, which is often to be guaranteed by the SSH designer.

There are three issues regarding the design of the SSH which are described below:

I) The fouling behaviour of coal fly ash compositions in syngas streams produced by different coal gasification plants is different and depends on the composition of the gasified coal and on gasification plant operation conditions.

II) The fly ash is very sticky at high temperatures compared to lower syngas temperatures. Conventional SSHs are located at the highest syngas temperature zone and are therefore prone to significant fly ash deposition.

III) The Syngas flow mal-distribution is worst at the SSH inlet because it is located just downstream the sharp bend of the junction between the upwardly tilted hot syngas Transfer Duct and the vertically downwardly oriented SGC channel .

US2009/0151250 discloses a system for recovering heat from a syngas and producing power therefrom. The system comprises a cooler including three or more heat exchangers or heat exchanging zones arranged in series. The raw syngas via a line is cooled by indirect heat exchange in the first heat exchanger. The cooled raw syngas exiting the first heat exchanger via another line can be further cooled by indirect heat exchange in the second heat exchanger. The cooled raw syngas exiting the second heat exchanger via yet another line can be further cooled by indirect heat exchange in the third heat exchanger ("third zone") .

The system of US2009/0151250 is directed to relatively small scale gasification systems. The system is designed to process waste. The feedstock comprises a mixture or

combination of two or more polymers, biomass derived

materials, or by-products from manufacturing operations. The feedstock can include one or more carbonaceous materials combined with one or more discarded consumer products. The small scale enables the use of separate heat exchanger units, connected via lines. The third heat exchanger is an

"economizer". Anyone or all of the heat exchangers can be shell-and-tube type heat exchangers. At least a portion of the superheated steam can be directly supplied to one or more steam turbines to produce power.

However, the above described features render the system of US2009/0151250 unsuitable for the processing and cooling much larger scale, higher throughput coal gasification systems. Higher throughput herein means, for instance, in the order of 80 to 90 kg/s of syngas throughput. Small scale is in the order of 10 kg/s of syngas or less. The feedstock of the US2009/0151250 system typically produces tar, which is removed from the gasification reactor, whereas the syngas is relatively low on ash. Coal gasification on the other hand has ash related issues, as described above. The shell-and- tube heat exchangers, as well as the lines connecting the individual heat exchangers, would clog due to the sticky ash issues relating to coal gasification.

There is a need for an improved syngas cooling assembly with a Steam Super Heater (SSH) that is less prone to fouling by deposition of fly ash particles and getting a more uniform syngas flow distribution thereby improving and stabilizing the SSH performance.

SUMMARY OF THE INVENTION

The disclosure provides a syngas cooling assembly for cooling a hot syngas comprising ash, produced by a

gasification reactor, the assembly comprising:

a syngas cooling channel;

a first heat exchanger arranged inside the syngas cooling channel; and

a Steam Super Heater (SSH) heat exchanger arranged inside the syngas cooling channel, downstream of the first heat exchanger .

According to another aspect, the disclosure provides a method for cooling a hot syngas comprising ash and produced by a gasification reactor, the method comprising the steps of:

providing a syngas cooling channel;

arranging a first heat exchanger inside the syngas cooling channel;

arranging a Steam Super Heater (SSH) heat exchanger inside the syngas cooling channel, downstream of the first heat exchanger; and inducing the hot syngas to flow through the syngas cooling channel.

The hot syngas may be generated by partially combusting a coal, heavy petroleum residue and/or biomass containing carbonaceous feed in the gasification reactor. The hot syngas may flow from the reactor via an upwardly tilted hot syngas transfer duct into an upper end of a substantially vertically oriented tubular syngas cooling channel. The SSH and other heat exchangers cool the syngas from a temperature typically above 700°C to a temperature typically below 350°C. Herein the Steam Super Heater (SSH) heat exchanger may cool the syngas by bringing saturated steam in a superheated condition and at least one of the other heat exchangers may cool the syngas by water evaporation.

Advantages of the arrangement of the Steam Super Heater

(SSH) downstream of another heat exchanger are that:

I) The temperature of the superheated steam produced by the SSH is more stable and can be predicted with a higher accuracy .

II) By relocating the Steam Super Heater (SSH) to a position downstream of a small evaporator heat exchanger, which is also identified as a H2O-EVAP bundle, the syngas flow entering the SSH will be considerably more uniform. This relocation is critical with respect to the strong vortexes just downstream the junction of the Gas Reverse Chamber

(GRC) . In the heat transfer correlation and thermal design software the syngas flow upstream the Steam Super Heater (SSH) is assumed to be uniform. The conventional location of the SSH upstream of the other heat exchangers therefore brings uncertainty in the theoretical calculations.

Ill) One of the main factors which causes the

underperformance of the SSH is the fouling. In the current configuration the SSH is the first heating element with horizontal tubes which is facing the hot syngas flow.

Therefore, it is the first place which the flyash starts settling, also in view of local recirculation/backflow .

Because s H ₂ O-EVAP heat echanger bundle is less sensitive to fouling and partial blockage than the SSH, it would be less risky to have the syngas first flowing through an H ₂ O-EVAP heat exchanger bundle before entering the SSH. Any

underperformance of the first ¾0-EVAP heat exchanger bundle is compensated by the other ¾0-EVAP heat exchanger bundle (s) downstream of the SSH.

IV) The syngas temperature at the inlet of the syngas cooler is very high, typically above 700°C . Therefore, the flyash is in its stickiest condition. The risk of high fouling, leading to partial blockage at this location is therefore high. By relocating the SSH to downstream the first

H20-EVAP heat exchanger, the risk of SSH fouling will be less because the syngas temperature is lower.

In addition to the above, the assembly and method of the disclosure allow efficient cooling of high throughput

sysngas, in the order of 80 to 90 kg/s of syngas throughput or more. The reduced fouling limits downtime for maintenance, thus also reducing operating costs.

These and other features and advantages of the method and system according to the invention will be apparent upon reading the following detailed description of embodiments depicted in the accompanying drawings and the accompanying claims and abstract.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate

corresponding parts, and in which: Fig. 1 shows a gasification reactor equipped with a syngas cooler assembly according to the invention; and

Fig. 2 shows a prior art syngas cooler assembly. DETAILED DESCRIPTION OF DEPICTED EMBODIMENTS

Figure 1 shows a gasification reactor 1 for the partial combustion of a carbonaceous feed, such as coal, heavy petroleum residue and/or biomass, to produce synthetic gas, also known as syngas.

The gasification reactor 1 comprises a reactor chamber with a cooled membrane wall. Via the lower end of the reactor 1 hot viscous slag drips into a slag collection bath (not shown) . Via the upper end of the reactor 1 hot syngas, comprising Hydrogen (¾) and Carbon Monoxide (CO) , is vented into hot syngas quench pipe 2. The reactor 1, the slag collection bath 4 and the hot syngas quench pipe 5 are encased in a pressure vessel (not shown) .

The quench pipe 2 is connected to a tilted hot syngas Transfer Duct 5, which which cools down the Syngas by

recycling the a part of cooled Syngas which is downstream the Syngas Cooler outlet. The quench Syngas is introduced to the quench pipe by recycling Compressors, not shown on the picture. By mixing the recycled syngas and the syngas coming out from the Gasifier the syngas temperature drops down from e.g. 1600 °C to 900 °C. The quenched syngas then flows into an upper part of a substantially vertically oriented tubular syngas cooler channel 11 with a closed dome shaped cap 12 containing a Gas Reverse Chamber (GRC) 40 and a funnel-shaped lower end 13, which discharges the cooled syngas into a cooled syngas discharge conduit 14. The tilted hot syngas Transfer Duct 5 is arranged at an acute angle, acute being smaller than 90 degrees, with respect to the vertical orientation of the syngas cooler channel 11. The acute angle may be in the range of about 30 to 60 degrees, for instance in the order of 45 degrees.

The SynGas Cooler (SGC) channel 11 is equipped with a syngas cooling assembly 15-18 comprising several heat

exchangers 15-18. Each heat exchanger may comprise a series of nested substantially co-axial heat exchanger conduits that are supported by a corresponding support frame (not shown) within the syngas cooling channel 11. For instance, the heat exchangers may comprise several coiled heating surfaces, comprising coiled conduits. The coiled conduits or coiled heating surfaces may be referred to as coiled heating surface elements .

The heat exchangers comprise a Steam Super Heater heat exchanger 16, which is also identified as the SSH. The heat exchangers may also include a number of, for instance three, other heat exchangers 15, 17 and 18. The assembly comprises a first heat exchanger 15. The first heat exchanger is followed by the SSH 16. The SSH is followed by at least one second heat exchanger 17, 18. Optionally, the system may also include one or more Economizers (not shown) arranged below, i.e. downstream of, the lowermost heat exchanger 18.

In the Steam Super Heater (SSH), 16 the syngas is cooled by heating saturated steam in the SSH heat exchanger conduits to a temperature typically around 400°C, thereby bringing steam in a superheated condition. In the, for instance three, other heat exchangers 15, 17 and 18, the syngas is cooled by evaporating water in the heat exchanger conduits. The other heat exchangers are therefore also identified as Evaporators or H ₂ 0-EVAP1, H ₂ 0-EVAP2 and H ₂ 0-EVAP3.

The heat exchanger conduits of the SSH 16 are fed by saturated steam which is coming via steam supply conduit 23 from a steam and water supply and re-circulation drum 20 and after superheating delivered to the steam turbine or process equipment via conduit 24. The heat exchanger conduits

evaporators 15, 17 and 18 are fed by saturated water via downcome conduits 21, 25 and 27 and after partial evaporation in the heat exchanger tubes, by the risers 22, 26 and 28, recycled to the drum 20. In the drum 20, steam is separated from water and water is recirculated by a recirculation pump assembly 30 back to the evaporators 15, 17 and 18.

The feed water, which is coming from high pressure pumps, is preheated in the economizer and then it goes to drum 20. The water is recirculated in the drum by recirculation pump(s) in the evaporator system to produce a water-steam mixture. The mixture of water and steam is separated in the drum. The saturated steam is getting dry through the

separators and steam dryer, and then the dry steam goes to the SSH.

Additional cooling water is supplied to the drum 20 via a feed water pump and feed water supply conduit 31.

In accordance with the disclosure, the SSH 16 is

positioned downstream of one of the other heat exchangers 15 when seen in the direction of the syngas flux F. This has the advantage that the syngas flux F when it reaches the SSH is less turbulent and has lost at least some fly ash or other fouling generating components, so that the SSH performance is optimized and stabilized.

Figure 2 shows a conventional syngas cooler assembly 111 in which the Steam Super Heater (SSH) 116 is located above and upstream of two other heat exchangers 115 and 117 in which water is evaporated and that are therefore also

identified as H ₂ O-EVAPI&2. A disadvantage of this

conventional prior art syngas cooler assembly 111 is that the hot syngas has a turbulent flow regime illustrated by arrows 120 and contains fly ash that is deposited on the tube surfaces of the SSH. It will be understood that by converting the conventional syngas cooler assembly 111 into the improved Syn-Gas

Cooler (SGC) assembly 11 shown in Figure 1, as illustrated by the arrows 122 in Figure 2, the syngas flux F, when it reaches the SSH 16, has already lost some turbulence and fly ash since at least some turbulence and fly ash are removed by the upstream heat exchanger 15, thereby optimizing and stabilizing the performance of the Steam Super Heater ( SSH) 16.

The disclosure is not limited to the above described embodiment thereof, wherein many modifications are

conceivable within the scope of the appended claims. Features of respective embodiments may for instance be combined.