Customised revamping of steam methane reformers

STEAM METHANE REFORMING

Customised revamping of steam methane reformers

When revamping the steam methane reformer, a detailed analysis of the whole reformer by an experienced technology licensor with deep plant knowledge is required to achieve the best solutions. Casale presents two case studies which provide examples of what can be achieved when following this approach.

Nowadays, revamping of the steam methane reformer (SMR) is the simplest way to increase plant throughput or reduce plant energy consumption, which in turn contributes to CO2 footprint reduction.

In Casale’s experience, SMR revamping is an activity often required by its clients many times and with ever increasing frequency.

Statistically, it is not uncommon to find a furnace that has been pushed beyond its upper throughput limit. Many critical components of the steam reformer unit, such as the catalyst tubes, pigtails, intermediate tube sheets and shield coils are inevitably forced to operate very close to their material design limits.

In addition, many other limitations can be experienced over the years due to aging of the reformer components, misoperation, the original design, or new environmental emission requirements.

In many cases, conditions that were already critical can be exacerbated when improvement modifications or revamping activities are carried out, particularly when the plant owner does not request a licensor assessment, which is fundamental to minimise risks and avoid any subsequent surprises on plant consumption figures.

There is a timeframe before a point of no return when symptoms or warning signs can be identified in time and with good reliability, avoiding unplanned outages and potential risk to plant personnel. This is the starting point or the first step toward the revamping stage.

Based on Casale experience, it is essential to identify where abnormal conditions, design limitations or upset operating parameters are located. It is crucial that this investigation shall be conducted through a whole reformer detailed data analysis to be carried out by a technology licensor with a deep plant knowledge background.

The following two project cases demonstrate the importance of carrying out a detailed data analysis of the whole reformer as well as Casale’s capability to customise the revamping scheme and technological solution to the existing steam reformer design, targeting the required objectives.

Fig. 1: Primary reformer convection section original arrangement

Fig. 2: Primary reformer convection section revamped arrangement

Fig. 3: New steam super heating coils (hot and cold) supplied by Casale

PHOTOS: CASALE

Fig. 4: Upper hood of the convection section

PHOTOS: CASALE

Case 1

Casale was awarded an EP project for an ammonia plant revamp to reduce energy consumption.

Many limitations were found in the primary reformer convection section in addition to the biggest one related to the air preheater (APH) which was an old rotary type. The reformer was an induced-draft, top-fired type with an omega convection section configuration and an integrated auxiliary boiler (see Fig. 1).

During the past, the client had had a lot of issues related to the rotary type APH, mainly related to corrosion issues. Many maintenance activities had been performed on the APH in order to mitigate the overall underperformance of the steam reformer prior to making the decision to approach Casale.

Analysis

After a campaign of data collection, an overall detailed analysis of the primary reformer was performed, and the original reformer design was verified.

It was found that, besides the rotary APH, there were some other issues that needed to be addressed that the client was not aware of.

For example, it was discovered that both the steam superheating coils (hot and cold) were underperforming and were unable to achieve the desired process steam outlet temperature despite the flue gas temperature being higher than the required temperature.

Based on Casale’s experience, this primary reformer section was in a very critical condition and subject to mechanical degradation, accelerated by operating conditions, which normally lead to minor or major underperformance of the coils. This phenomenon was made worse by the practice to compensate for the temperature drop by increasing the combustion heat release of the steam superheating burners.

Some other issues were found with regard to the residual life of some components of the reformer, like the high-grade nickel intermediate tube sheets.

Solution

Many modifications to the reformer were required, such as the installation of new hot steam superheating coils as complete modules (Fig. 3), the replacement of the rotary APH with a new more efficient plate type APH with relevant duct modifications, and finally, rebalancing of the heat recovery into the convection section cold leg in a more efficient way, thereby reducing the overall steam consumption required by the reforming reaction.

It was also possible to reduce the required duty of the BFW preheater coil, whose surface was partly replaced by a new coil, with the purpose to “cold” preheat the feed to the HDS section, shifting the heat from the steam system to the more valuable feed preheating system.

Of course, this modification required a more detailed assessment of the steam reformer radiant chamber to prevent any mechanical issues due to the new operating conditions.

Another challenge was from a mechanical viewpoint, due to the one-month timeframe imposed by the client to install the new items withing the turnaround.

All items were prefabricated as much as possible, and all interventions were studied and engineered targeting the required constraints such as the stiffening of the upper hood of the convection section, which was removed in a single piece (Fig. 4).

Thanks to the solutions found, the overall installation was performed according to the requested one month schedule.

All of the issues concerning the steam reformer were successfully addressed and solved, resulting in an energy saving of 9,000 t of the fuel consumption per year, which in turns equates to a carbon footprint reduction of 24,000 t of CO2 per year.

Case 2

Casale was awarded an EP project for an ammonia plant revamp to increase capacity from 1,800 t/d to 2,000 t/d.

A detailed assessment of the plant revealed some limitation in the primary reformer convection section and the radiant chamber.

The reformer was an induced-draft, top-fired type with an omega convection section configuration and an integrated auxiliary boiler (Fig. 5).

Fig. 5: Primary reformer convection section original arrangement

Fig. 6: Primary reformer convection section revamped arrangement

Analysis

A detailed analysis of the primary reformer was performed, and the original reformer design was verified against the current operation. It was found that both the mixed feed coils and the process air coil, were significantly underperforming and the radiant chamber and the combustion system was verified to be unsuitable for the future increased plant capacity.

Solution

During the engineering phase many parameters around the reformer were analysed in order to minimise the intervention. Thanks to an overall plant assessment and optimisation, the modifications required to target the project scope were limited to a new design of the catalytic tubes and radiant chamber outlet system as well as a new design for a new mixed feed coil and a new “cold” process air coil (Fig. 6).

The new design, together with the newly achieved process parameters, resulted in no modifications being required for the combustion system and burners. In addition, the new design provided a safety margin for the existing design, especially for the reformer inlet system, for any conditions, including higher capacity.

The overall steam consumption required for the reforming reaction and internal plant use was decreased and optimised. In this way, it was possible to reduce the required duty of the BFW preheater coil, whose surface was partly replaced by a new coil, with the purpose to “cold” preheat the process air so that the surface of the existing “hot” process air coil could be used to provide the extra duty required by the increased plant capacity. This more cost-effective solution permitted the performance of the existing process air coil to be restored without impacting its design.

Another challenge was represented by the geometrical constraints of the mixed feed coil which required more surface to be installed within the same layout. In addition, the client requested a solution to minimise the intervention within a timeframe of only two weeks.

A dedicated design was developed, the so-called Casale “pre-assembled” design which permits the complete coil bundle installation (tubesheets, hairpins, manifolds, etc.) with a once-through solution (Fig. 7). This solution preserves the existing system, minimising the required site modifications such as cutting of the reformer wall casing (when there is no splice), refractory dismantling and reinstallation, etc.

Thanks to the solutions found, the overall installation was performed according to the requested two week schedule. All of the issues concerning the steam reformer were successfully addressed and solved resulting in an energy saving of 1,700 t of the fuel consumption per year, which in turns equates to a carbon footprint reduction of 4,400 t of CO2 per year.

Fig. 7: Mixed feed coil supplied by Casale

PHOTO: CASALE