Revamps 2023 Issue

300

250

200

150

Before cleaning

After cleaning

100

March

April

May

June

July

August

Figure 6 Stack temperature before and after cleaning

The convection section evaluation (see Table 2 ) reflects the most widespread design with the following bundles (from top to bottom): economiser, upper steam generation, steam superheating, and lower steam generation (example under the same firing rate). Case study: revitalising HGU performance An Egyptian oil refinery, in operation since 1999, has faced challenges with its hydrogen generation unit (HGU) since 2005. Issues such as hot spots on catalyst tubes, ageing reformer tubes and outlet systems, and reduced hydrogen demand have led to the unit operating at a reduced capac- ity. To address these bottlenecks and evaluate the unit’s status, a comprehensive assessment and debottleneck study was conducted by the OEM. One significant finding of the study revealed the under - performance of the convection coils, which hindered the unit from achieving its desired efficiency. Over more than 20 years of operation, the convection coils, primarily con- sisting of finned tubes, suffered from increased fouling due

It is worth mentioning that these furnaces were designed to have 68.3-71.0% process duty of total absorbed duty (depending on whether it is SOR or EOR). If, for example, steam superheating coils are fouled, cleaning may reduce this ratio process/total duty. An additional indicator of this potential fouling consequence is the fact that almost no boiler feed water (BFW) is being used for attemperation (desuperheating). For this scenario, constant flow rates for process streams are assumed, but it is also possible to consider all the factors and heat balance changes for the entire system. ROV cleaning: catalytic reformer heater In configurations where a steam generator is only located in the convection section, such as catalytic reformer heat- ers, it is crucial to adjust flow rates and reflect changes in absorbed duty for each bundle that may result from clean- ing. Specifically, a steam drum should be included in the model to respond accurately to all changes in temperatures/ pressures of inlet/outlet streams.

to inadequate inspection and cleaning practices. The study recommended a potential solution of inspecting and robotically cleaning the external sur- face of the finned tubes to overcome this issue. On the advice of the OEM, IGS was contracted to perform Tube Tech’s con- vection section performance recovery service at a hydrogen production unit at the refinery. The project involved increasing the size of six existing access doors in the convection section and the robotic defouling of convection coils. The project commenced on March 29, 2023, and was completed on April 3, 2023. The original planned scope of work, which included defouling and door installation, remained unchanged throughout the project.

Convection section cleaning results for ethylene cracker

Parameter Fuel firing Fuel firing *

UOM

Before 5565 32.04 29.37 14.86 1,033

After 5655 32.64 30.56 15.02 1,037

nm³/hr

Gcal/hr (LHV)

Total abs or bed duty

Gcal/hr Gcal/hr

Radiant duty

BWT

°C °C °C °C °C °C %

Stack temperature

180 590 376 446 269

134 582 454 541 254

Radiant inlet CSS outlet HSS outlet ** BFW outle t

91.67 21.21

93.61 21.21

Overall efficiency

Process duty Steam duty

Gcal/hr Gcal/hr

8.16

9.35

* 1.5% of heat losses have been assumed, and 11% of excess air is calculated using the fl ue gas oxygen content. ** HSS coil has been evaluated assuming no BFW for desuperheating

Table 1

Revamps 2023