Panorama Editorials

Editorials

Pet-Coke Logistics - Transport and Storage

By Barry Woodbine, AUMUND Group

With finite fossil fuel reserves and ever escalating fuel costs every drop of crude oil extracted from the ground or from beneath the sea really is now like “Black Gold” and every ounce of energy it contains extracted to maximise the overall efficiency of the process.

Petroleum coke is a by-product of crude oil refinery operations and is literally “the dregs of the barrel”. Pet coke is a residue high in carbon content and low in hydrogen that is the final product of the thermal cracking of residual oil. After virtually all light and medium weight hydrocarbons have been removed from crude oil, a heavy residual oil remains. This material is then thermally cracked to recover more oils for use as gasoline and diesel products, the solid material that remains is sold commercially as petroleum coke. Pet-Coke has a calorific value slightly above most coals and may be handled in exactly the same manner requiring no specialised machinery or equipment. Worldwide around 100 million tons of marketable pet coke is produced, mostly for fuel although a significant volume is diverted for anode production and other industrial uses.

The price of Pet-Coke follows in principle the price of coal and trading volumes are substantially effected by Mediterranean consumers buying Pet Coke from the US east coast ports to displace coal imported from South Africa, such is the typical trade that has developed now worldwide for this once low priced waste material. Pet Coke is often the fuel of choice for cement manufacturers replacing more expensive coal with relative little modification to kiln or burners.

For local consumption Pet-Coke may be shipped by rail and road but for the bulk of movements now deep sea shipment in Handymax sized vessels represents the core of the international trade. Most refineries with established Pet-Coke export business will have dedicated port facilities for storage and ship loading but where such facilities do not exist the refiner or shipper must make provision to use existing wharfs or jetties and often that implies bringing in mobile ship loading equipment, such as that manufactured by B&W Mechanical Handling Limited (AUMUND Group) in the UK, in order to utilise an existing multipurpose berth that otherwise may be handling other commodities.

Such a scenario applied in the US at the Port of Wilmington, Delaware, founded in 1923 the port has a full-service deep water facility, draft of around 12 metres, and marine terminal handling about 400 vessels annually with an annual import/export cargo tonnage of over 4 million tons and is the busiest port of the Delaware river.

Located at the confluence of the Delaware and Christina Rivers, 65 miles from the Atlantic Ocean, the Port is owned and operated by the Diamond State Port Corporation of the State of Delaware. In the same general locality the Delaware City Refining Company has restarted the former Valero refinery from which Pet-Coke will be produced and transferred by rail wagon to the Port for storage and export.

Port Contractors Incorporated (PCI), operating from Wilmington, will receive the coke to their dry bulk cargo facility at 501 Christiana Avenue, adjacent to the Port, using a fully enclosed rail wagon discharge system into their new dedicated 100,000 square foot storage facility. The off port storage facility will allow Pet Coke to be accumulated from rail wagon deliveries providing sufficient capacity for at least one vessel loading, in this manner the outloading operation performance is not effected by any inland transportation delays.

Since the berth that PCI intended to use for Pet-Coke exports would also be used for other port operations it was necessary the ship loading equipment should be mobile and able to be cleared off the berth when not required. The B&W Mobile Shiploader was the ideal solution offering high performance and relative economy in operation, compared to mobile harbour cranes already operating at site. Since commissioning the mobile Shiploader has achieved a peak loading rate of 1,500 tons per hour and an average through the ship performance of around 1,200 tons per hour comfortably exceeding what would be possible with the other options available and at a much lower operating cost.

For this application the Shiploader was supplied with a mobile “Kleen-Line” belt feeder designed to receive material from wheeled loaders working from a quayside stockpile. During the vessel loading operation the Pet Coke is transferred from the new covered storage facility to the berth using a fleet of tipping trucks working on a merry-go-round basis and dumped to the quayside stockpile ready for immediate loading. Both the Shiploader and Kleen-Line feeder are provided with towing facilities such that they may be easily moved around the berth by wheeled loader of fork lift truck for vessel trimming and movement to storage.

It is very likely the Pet Coke will be destined for the Mediterranean area and perhaps will be imported to the Port of Cadiz (Spain) and hauled by truck, working on a merry-go-round basis, up to the Jerez plant of the Holcim Group as kiln fuel for their cement plant. At the plant the Pet Coke is discharged directly from the tipping trucks into a surface mounted SamsonTM feeder providing a buffer holding capacity and a controlled rate discharge to an inclined belt conveyor. The conveyor is fitted with an overband magnetic separator, to remove tramp ferrous metals, and discharges to a Circular Storage stacker and reclaimer system by Schade (Aumund Group since 2001).

The storage facility is fully enclosed with a dome cover and comprises a radial stacking boom mounted to a central slew ring and designed to generate a semi-circular shaped stockpile automatically by level and positional detector signals working within a pre-set zone. A cantilevered boom chain scraper style reclaimer draws the material down from the inner stockpile face to a central outlet from which it is transferred by belt conveyor to the fuel mill bunker system. This is a fully automated system and the stacker and reclaimer booms operate continuously allowing material intake and recovery simultaneously. The operating zone of the stacker boom is linked to the reclaimer such that there can be no overlap and the two operations may run continuously working around the central column without interruption.

Generally the storage will be sized to accommodate the most economical shipment and for Handy size vessels this will be typically in the range of 40,000 tons plus a reasonable spare capacity to give some flexibility in vessel arrival timing.

Both the stacker and the reclaimer are mounted to slew rings on the central vertical column which supports the complete stacker/reclaimer and is extended upwards and, via another slew ring, supports the incoming conveyor head such that there are no imposed loads applied to the dome structure allowing use of a light weigh Geodesic design. The circular storage with Geodesic dome represents the most economical solution in these applications with the lowest footprint per ton stored and is entirely suitable for both cement and power plant.

There are many such applications with the pet coke import to an existing berth using mainly geared vessels with grabs to discharge the cargo to trucks via typically a mobile hopper or Eco-Hopper where dust control is critical. Such a system will unload around 500 tons per hour average through the ship with say two cranes working. This will require an average intake capacity of 600 tons per hour to the radial stacker equating to a truck discharge spot rate of say 900 tons per hour.

Whilst the circular storage is ideal for a single commodity it is not suitable for segregated stockpiles and multiple use of the same storage building for different fuels and also perhaps additive materials. In a cement plant for example it may be necessary to store coal and or Pet Coke plus additives such as iron ore, gypsum, trass and others depending on the plant process demands. In this situation the Semi-Portal reclaimer by Schade with segregated storage bays and overhead distribution conveyor system is ideal. With the Semi-Portal design the reclaimer has the usual chain scraper boom system discharging to a longitudinal conveyor but in this case the reclaimer boom is supported to an overhead frame and may be raised up to clear the storage bay dividing walls. In this manner the same Reclaimer may be travelled along the storage building to the selected bay from which fuel or additions material is recovered and conveyed to the appropriate mill bunkers.

A common SamsonTM feeder system may be used to intake and handle the whole range of fuels and additive materials and the travelling distribution conveyor aligned to the appropriate storage bay avoiding any cross contamination.

The intake and reclaim systems are automated allowing simultaneous operation within defined working criteria, it is not possible to load and reclaim from the same bay at the same time and therefore the materials management system must accommodate this, and, interfacing to the fuel and raw meal mill bunkers must ensure the mills never run short of fuel or any constituent in the raw meal mix. Such control programs are part of the storage management system and may be included in the Schade supply package along with the necessary feeders and conveyor equipment from intake to mill bunkers and even at the bunker discharge where the AUMUND CentrexTM solution may be applied to such as Synthetic Gypsum which is notoriously difficult to extract from hoppers or silos and prone to bridge and block with the slightest provocation.

Where the cement or power plant is inland then truck haulage from the port direct to the user may not be appropriate and some form of on-port or local storage may be required. In fact the exact opposite to the situation on the Delaware where storage is required for fast ship loading, in this case storage is required for fast ship discharge to avoid high demurrage costs. In an ideal world of course the ship discharge system would be linked by belt conveyor to local storage on or close to the port or berth. In this situation, using geared vessels, a dedicated finger jetty with Eco-Hoppers on rails and a central collecting conveyor is the accepted solution where there is no existing port facility or river berth.

Using an existing port with multi-purpose berth with larger vessels not fitted with deck cranes then a mobile harbour crane plus a mobile Eco-Hopper is a suitable solution either transferring the Pet Coke to local storage by conveyor or, for maximum flexibility, using truck haulage on a merry-go-round basis loading to off port open storage. Again this is the exact opposite to the Delaware situation and taking this reverse analogy further the Pet Coke may be loaded to rail wagons for inland distribution from the off-port storage area.

Such a system is employed at the port of Port of Jorf Lasfar in Morocco where solid fuels are imported through the existing port using existing grab fitted harbour cranes and truck loading hoppers plus an off port storage area serviced by a B&W (AUMUND Group) StormajorTM mobile stacker to create a large stockpile. The stacking area holds 40,000 tons including both coal and Pet Coke which is sufficient to provide a buffer for both ship loading and distribution.

Fuel is recovered from the stacking area by wheeled loaders and transferred via a fixed conveyor system to a rapid rail wagon loading bin for inland distribution to the three Holcim cement plants within Morocco. The trains could be loaded using the wheeled loaders direct or via the StormajorTM but using a rapid loading bin reduces the train loading time and provides a weighed volume to each wagon thus eliminating any risk of overloading requiring costly manual evacuation. Due to the success of this contract with Holcim B&W received an order for a near identical Stormajor from Holcim’s neighbours, Ciments De L’Atlas, who are also located at the Port of Jorf Lasfar in Morocco. For this later delivery the client elected to include powered travel in the machine specification allowing the StormajorTM to be rapidly moved around the stockpile area. The flexibility of using truck transfer from the import berth allows both cement operators to share a common import facility but with independent off port storage and distribution arrangements. There are many installations around the Mediterranean where pet coke is imported through existing facilities and transported inland by road truck but of course where there is rail connection to the port and the end user this is always the most economical and least polluting option.

Looking further afield B&W have recently commission one of their SamsonTM Under Rail (SUR) intake systems to the Holcim Group plant Cementos Minetti S.A. in Argentina. Argentina is a major producer of pet coke from the La Plata area and with excellent rail connections and export facilities. The SUR pet coke intake unit is similar to that supplied originally to Cementos Balboa in Spain (as pictured herein) and offers significant advantages with a much reduced excavation depth and reduced material free fall consequently minimum degradation and dust generation.

Flexibility at the port for both import and export facilities combined with professional intake and storage facilities at the cement and power plant enables the AUMUND Group to offer the most appropriate combination of solutions at every stage of the logistic chain from producer to consumer and at all stages between.