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Feb-2022

Optimising processes and operations for CO2 emissions reduction

A proactive approach can achieve immediate CO2 emissions reduction with almost no investments while reducing operating costs.

MARCELLO FERRARA
ITW

Viewed : 575


Article Summary

Global warming concerns have led public opinion and policy makers towards stricter control and reduction of CO2 emissions. Many actions are taking place and are planned to achieve this target. Most of these actions are against fossil fuels, so the oil and gas industry may be badly impacted in the long run. According to reports, in 2019 annual CO2 emissions from oil were almost 12 billion tonnes. This adds to the general sentiment that perceives the oil and gas industry as polluting the environment, while not recognising its key role in the development and well being of humankind.

On the other hand, in the current scenario of economic depression, the oil and gas industry is recovering from years of low margins when investments were dramatically reduced. There is therefore the need to comply with the targets of CO2 emissions reduction while not having the size of investments that were available years ago. Process optimisation is one of the keys to matching legal requirements while making only minor investments, provided a mind shift takes place in the industry.

Global warming concerns have led public opinion and policy makers towards stricter control and reduction of CO2 emissions. Many actions are taking place and are planned to achieve this target. Most of these actions are against fossil fuels, so the oil and gas industry may be badly impacted in the long run.

According to reports, in 2019 annual CO2 emissions from oil were almost 12 billion tonnes. This adds to the general sentiment that perceives the oil and gas industry as polluting the environment, while not recognising its key role in the development and well being of humankind.

On the other hand, in the current scenario of economic depression, the oil and gas industry is recovering from years of low margins when investments were dramatically reduced. There is therefore the need to comply with the targets of CO2 emissions reduction while not having the size of investments that were available years ago.

Process optimisation is one of the keys to matching legal requirements while making only minor investments, provided a mind shift takes place in the industry.

This article illustrates some possibilities for reducing CO2 emissions through process and operations optimisation, while achieving overall cost reductions with almost no investment. Needless to say, the article provides only order of magnitude numbers while actual figures can be determined by a single operator/site, based on its specific situation.

Immediate implementation of such optimisations, besides achieving overall cost reduction, may result in an immediate reduction in CO2 emissions, thereby substantially improving the environmental balance sheet.

ITW Online Cleaning
The current mindset of the oil and gas industry is to postpone any cleaning activity until it is urgently needed, because cleaning is associated with mechanical cleaning which is time consuming and leads to huge downtimes. Therefore, a decay in performance will be tolerated because it has already been included in the budget. It is not uncommon to see fouled preheat trains of CDUs leading to furnace inlets decrease by 10°C or more in a year. When the furnace inlet temperature decreases, this has to be offset by an increase in fuel firing in order to achieve the target furnace outlet temperature, which translates into increased fuel consumption and hence increased CO2 and airborne emissions.

The above is based on the huge downtime needed for cleaning a preheat train, say 15-20 days depending on the number of exchangers, so it has historically been more profitable to tolerate energy losses rather than impact production. This mindset can no longer be applied in light of reduced margins (hence the need to find ways to reduce costs which are not simply based on reducing spending money), emission taxes, and environmental compliance.

ITW Online Cleaning performs the cleaning of an entire production unit in 24 hours on a feed-out/feed-in basis. This creates new opportunities for increasing value.

If every year a 100 000 b/d CDU makes a pit stop to clean the hot preheat train, because the CDU has two preheat lines, the refinery can clean one line at a time without theoretically interrupting production. The mechanical cleaning of one preheat line takes 15 days, with the unit running at about 50% capacity. The cleaning of two trains takes therefore 30 days, with the unit at about 50% capacity. This corresponds to 15 days’ production loss every year.

We propose replacing the pit stop with regular Online Cleaning. ITW Online Cleaning is performed by only one or two engineers. The refinery can take advantage of:
•    Increased production (with related margins)
•    Reduced fuel consumption
•    Reduced CO2 and airborne emissions
with an ROI > 40:1.
The input data are:

Furnace inlet temperature (clean)            240°C
CO2 emissions cost                                80 $/T
Feed CP                                   0.55 Kcal/(kg°C)
Fuel gas lower heating value        8200 Kcal/kg
Fuel gas cost                                         700 $/T
Operating margin                                     95 $/T
Kg CO2/kg methane                                2.75    Furnace efficiency normal run 80%

Furnace efficiency with regular Online
Cleaning                                                   85%   

This assumes a higher furnace efficiency in regular Online Cleaning mode because the lower furnace firing achieved as a result of a stable increased furnace inlet temperature will create less coke deposition inside the coils (and a lower skin temperature). Lower firing arising from a stable higher furnace inlet temperature will reduce the average skin temperature, and hence the hydrocarbons flowing in the outer portion of the coils will be subjected to an average lower temperature and will degrade less, thereby reducing their tendency to coke formation. This will give the benefit of increased furnace reliability and coil life, besides reducing the need for decoking.

Over two years, the benefits are around $90 million and CO2 emissions are reduced by about 32500 tonnes.

Case study
A vacuum unit was running as per normal operations until a change in feedstock led to destabilised asphaltenes and created massive precipitation in the preheat train. As a result, the normalised furnace inlet temperature dropped from 247°C to 219°C, while reducing capacity significantly. ITW was requested to perform Online Cleaning on an emergency basis in order to reduce refinery losses.

The job was performed in 24 hours on a feed-out/feed-in basis, and less than 48 hours spec-to-spec. Upon resuming full production, the furnace inlet temperature recovered almost to start-of-run conditions.

Upon considering the increased feed rate, the normalised furnace inlet temperature average increase was 47°C. Figure 1 summarises the achieved results. Figure 2 shows the achieved reduction in specific fuel gas consumption.

Following the recovery in furnace inlet temperature, average specific fuel gas consumption fell by 1.67 Mm3/h/t. By considering a feed rate of 400 t/h, the saving corresponds to a theoretical yearly CO2 saving of about 30000 tonnes, as well as about $7.5 million in fuel.

A point to note in Figures 1 and 2 is that performance following Online Cleaning is better than normal running.


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