Reprinted from August 2017HYDROCARBON ENGINEERING

Davide Costa, Econova Corporate S.p.A., Italy, and Ulrich Nanz, Sandvik Process Systems, Germany, discuss the implementation of a new sulfur handling system at the Sarroch refinery in Sardinia.

LITTLE BYLITTLE

Reprinted from August 2017 HYDROCARBON ENGINEERING

A s with all technological advances, the move towards reducing the environmental impact of a particular process or industry is a journey, not a destination. For the oil and gas business, one of

the key milestones along this route was the introduction of desulfurisation technologies, and the impact has been substantial.

Up until the latter part of the last century, mining still accounted for most of the world’s production of elemental sulfur. Today, only a few mines remain and virtually all

elemental sulfur is sourced through recovery from sour oil and gas.

While this has delivered significant environmental benefits, it has also brought challenges of its own. Approximately 50% of the sulfur produced in this way is traded internationally for use in products such as fertilizers, metals, chemicals, rubber products, pharmaceuticals, etc. It therefore needs to be converted from its molten state into a form that is suitable for handling, transportation, storage and subsequently re-processing.

It is this solidification stage that is now the focus of attention for many processors looking to further reduce the environmental impact of refinery operations. In this article, the authors examine how one company is continuing to reduce its environmental impact through investment in the cleanest possible solidification technology.

Sulfur solidification upgrade from slates to granulesIn a project that has seen the complete upgrade of sulfur handling capabilities at its Sarroch refinery in Sardinia, Italy, Sarlux has commissioned sulfur specialist Econova Corporate to install a new solidification system based on Sandvik’s Rotoform® granulation technology.

The project represents the continuation of a relationship that extends back to 1991 when Sarlux installed two sulfur slating lines at the refinery, with a total capacity of 700 tpd. After 25 years of operation, turnkey plant supplier Econova has replaced the slating technology with a granulation system including three Rotoform high speed (HS) granulation units, each with a capacity of up to 300 tpd.

Sarlux observes the importance of environmental impact when investing in technology and plant upgrades. This focus on continual improvement makes the upgrade a significant milestone in the development of the refinery; a key benefit of premium quality granules is the minimisation of dust generation during downstream storage and handling.

Clean and efficient granulationEach Rotoform unit consists of a heated, cylindrical stator and a large perforated rotating shell that turns concentrically around the stator, depositing sulfur drops across a continuously running steel belt cooler.

A system of baffles and internal nozzles built into the stator delivers uniform pressure across the whole belt width, providing an even flow through all holes of the perforated rotary shell. This ensures that all granules are of uniform size, from one edge of the belt to the other. The circumferential speed of the Rotoform is synchronised with the speed of the belt, so drops are deposited accurately, consistently and without deformation.

The belt is cooled by water sprayed on the underside, while efficient heat transfer results in rapid solidification of the product. The fact that there is no contact between the molten sulfur and the cooling water means there is no cross-contamination.

Figure 1. From slates to granules.

Figure 2. Sulfur granules on a conveyor.

Figure 3. Rotoform HS unit with spray nozzles for release agent.

Reprinted from August 2017HYDROCARBON ENGINEERING

At the end of the belt coolers, the sulfur granules are deposited onto a collecting conveyor and enter the handling system with a temperature of less than 65˚C.

One benefit of this system is direct solidification from the melt, eliminating the energy and equipment costs associated with subsequent crushing. Cooling takes place within seconds, so very little vapour or gas can enter the atmosphere and little oxygen can penetrate the product. And the environmentally friendly, indirect water-cooling method means that the water can be recycled within the system, over and over again.

Each line is capable of operating independently of the others for maximum versatility and individual units can be stopped and started without affecting the others. This approach not only provides the ability to accommodate fluctuating throughput rates, but also means that lines can be taken out for planned maintenance without having to shut production down entirely.

Process technologiesThe efficiency of the process is enhanced by the use of two technologies, Sandvik's ProCool and ProForm. The former's function is to bring the sulfur down to the required processing temperature before it enters the granulation units. The liquid sulfur is pumped through a filter and then

conveyed through the ProCool unit, an air-cooled finned tube system.

Liquid sulfur in refineries usually has a temperature of approximately 150˚C, which is too high to yield satisfactory results from the granulation procedure as the optimal processing temperature for sulfur is about 125˚C. At this temperature, the viscosity of the sulfur is higher, which helps to improve the granule shape and create a positive impact on both granule quality and production management.

The second technology is ProForm, used to ensure maximum process efficiency and a premium quality end product. For this, a special release agent is applied across the belt ahead of the drop forming stage using an array of spray heads. The use of this agent eliminates the possibility of damage to granules on discharge, and creates the surface tension on the belt necessary to deliver the optimum granule form.

The ProForm system includes fully automated mixing of the chemical with water. The agent is applied to the steel belt by means of a number of self-cleaning nozzles that ensure maximum efficiency for low consumption of chemicals.

Quality granules for low dustThe end result of the new process is a consistently-sized, hemispherically-shaped granule with a number of advantageous physical properties, such as:

n Low friability and impact abrasion resistance (low visual dust generation).

n Good flow characteristics for handling. n A high angle of repose for maximum storage capacity. n Uniform size and good characteristics for blending. n Low moisture content. n Consistent quality, and stable properties over time.

Given that dust can be produced during processing, storage, loading and transportation, factors such as fines and friability are an extremely important environmental consideration, especially as the Sarroch refinery is based on an island. The ability to produce a granule of the optimum form was therefore a key requirement.

The granules are fully compliant with the requirements of a ‘premium quality’ granule as defined by the Sulfur Development Institute of Canada (SUDIC). According to the SUDIC definition, premium quality sulfur should meet the following specifications 21 days after forming:

n Mean size: between 2 and 4 mm. n Size distribution:

§ Less than 5% bigger than 4.75 mm. § Less than 2% smaller than 1.18 mm. § Less than 0.1% smaller than 0.3 mm. § 75% must be within ± 1 mm of the average diameter.

n Moisture: less than 0.5% by weight. n Friability:

§ Less than 1% fines (<0.3 mm) under stress level I. § Less than 2% fines (<0.3 mm) under stress level II.

n Bulk density: 1040 kg/m3 loose, 1200 kg/m3 agitated. n Angle of repose: not less than 25˚.

Figure 4. Deposit of sulfur drops across a continuously running steel belt cooler.

Figure 5. An example of the Sandvik ProCool.

n Compaction: § Below 0.2% fines by weight under static load. § Below 0.5% fines by weight under dynamic load.

The plant was specifically developed to comply with these specifications, solidifying sulfur, direct from the melt, in a form that is ideal for bulk storage and handling.

Turnkey sulfur solidification projectThe overall Sarroch refinery project – a turnkey sulfur solidification system including engineering, procurement and construction (EPC) – was carried out by Econova, one of Europe's leading companies for sulfur solidification and handling, and associated port logistic facilities. As well as undertaking major projects for third-party clients, the company also owns and manages two sulfur solidification plants of its own. Situated in Puglia and Sicily, Italy, these plants have a total installed capacity of over 380 000 tpy of sulfur.

Econova's expertise extends beyond the solidification stage, encompassing everything from the receipt of molten

sulfur from the SRU, to a complete range of downstream handling processes including the maintenance, operating and supervision management.

Econova’s scope of work included the complete renewal of the sulfur pit including a new heating system, the supply of all-new piping for molten sulfur, cooling water and steam heating, and the full solidification system from upstream ProCool equipment to the Rotoform lines and all ancillary equipment.

The project also saw the provision of a new control room with a programmable logic controller (PLC), motor control centre (MCC) and electrical cabins. As well as managing the process, the controls also include sophisticated hydrogen sulfide (H2S) and sulfur oxide (SOX) sensors. Downstream equipment included collecting conveyors (all enclosed) and dust suppression solutions at the various loading points.

Econova now operates and maintains the sulfur plant on behalf of Sarlux, with systems running 24/7, or in accordance with the needs of the refinery. Plant management and maintenance is a key aspect of Econova’s service and the expertise of its trained operators is critical to the smooth running and successful operation of the entire process, ensuring that Sarlux gains maximum benefit from its technology investment.

ConclusionThe upgrade project delivered significant improvements to Sarlux’s sulfur processing and handling capabilities, increasing both productivity and flexibility (the solidification systems can operate independently to accommodate fluctuations in demand), while at the same time reducing the environmental impact of the refinery. It is also representative of the company’s recognition of its environmental responsibility, which has seen a number of other major initiatives in recent years.

Figure 6. An arrangement of three Rotoform HS units on the factory floor.

www.processsystems.sandvik.com www.econovaspa.it