NEW SHORT CONTACT TIME PROCESSES UPGRADE RESIDUAL OILS AND HEAVY CRUDES

New short contact time carbon rejection technology has been developed for upgrading residual oils and converting heavier crudes into high-quality synthetic crudes.

The process, called discriminatory destructive distillation, or 3D, has been demonstrated in a Kansas refinery on feedstocks ranging from 13.5 to 30.6 API.

The 3D process and its spinoff, the millisecond catalytic cracking (MSCC) process, were introduced at the National Petroleum Refiners Association annual meeting, Mar. 17-19, in San Antonio by David Bartholic of Bar-co Processes Joint Venture.

For the past year, Coastal Derby Refining Co. has been operating a revolutionary, according to Bartholic, circulating fluid solids processing apparatus that can be run as either a 3D process unit, to virtually eliminate the residual oil component of crude, or as an MSCC process unit, to upgrade VGO and residual oils.

Because both of these processes circulate a fluid solid in a manner similar to the well known and commercially accepted fluid catalytic cracking (FCC) process, existing FCC-type units can be easily and economically converted to either 3D or MSCC operation.

The 3D process is a low-pressure, carbon-rejection residual oil treating process for preparation of gas oils for fluid catalytic cracking (or MSCC), hydrotreating, mild hydrocracking, or full hydrocracking, says Bartholic.

The process is also applicable, he says, to upgrading heavy crudes or tar sands bitumen to high-quality reconstituted crudes for world markets.

3D PROCESS DESCRIPTION

The goal of the 3D process is to distill, or vaporize, any hydrocarbon feedstock through contact with a hot circulating solid.

The catalyst/liquid contacting system is designed to:

• Minimize conversion of the 1,000- F. hydrocarbons

• Minimize secondary cracking of the thermally unstable molecules

• Destructively distill the low-hydrogen, high molecular weight, high-boiling molecules into a lower molecular weight, lower-boiling molecule, and a highly carbonaceous molecule that deposits on the circulating solid, commonly called coke.

This coke contains the majority of the downstream catalyst poisons such as metals, nitrogen, asphaltenes, and some heavy sulfur compounds. It is burned in the regenerator to supply heat to the circulating solid, which in turn is returned to the contactor to vaporize more hydrocarbon feedstock.

Bar-co suggests that an alternative for controlling the SO2 from the process for coastal refineries would be seawater scrubbing (see OGJ, July 1, p. 52). However, an SO,-reducing additive provided sufficient control in the commercial trials.

The 3D system is similar to an FCC system, but 3D is not a conversion process. It is a millisecond carbon rejection process that conserves hydrogen in the feedstock while removing the majority of catalyst poisons.

Typical downstream catalyst poison removal/conversion percentages are as follows:

• Metals-90% +

• Nitrogen-40-70% (from 650+ F. material)

• Sulfur-30-50% (from 650+ F. material)

• Asphaltenes-90% +.

The 3D process is a new, economically attractive, commercially proven circulating fluid solids decarbonization-demetallization process for upgrading the bottom of the barrel.

COMMERCIAL OPERATIONS

In 1989, Coastal Corp. revamped its idle 10,000-b/d, 1952-vintage stacked FCC unit (FCCU) at its El Dorado, Kan., refinery to operate in either the 3D process or MSCC process mode.

During commercial testing of the 3D process from mid-April to mid-December 1990, the unit feedstock varied considerably (Table 1). The unit also processed about 30,000 bbl of emulsified oil to recover the oil.

All of the products produced in the 3D process unit were further upgraded with the crude unit intermediate products in existing refinery equipment.

3D PROCESS RESULTS

Tankage was made available so that the 3D process could be operated with either whole crude or the atmospheric tower bottoms (ATB) from that whole crude.

The 3D products from ATB and crude operations were analyzed and a comparison was made between ATB products blended with virgin 650- F. products and the 3D products produced from the whole crude operation.

All of the 3D fractions had lower API gravity and higher sulfur, nitrogen, and aromatic contents than their equivalent virgin fractions. This is to be expected because the major source of the cracked material transferred to the lighter cuts is from the 1,0001+ F. fraction of the feedstock.

The data also indicated that the 3D process does not convert hydrocarbon feedstock boiling below approximately 1,000 F., and that the virgin gasoline and distillate essentially go through the unit untouched so that there is no penalty for operation on whole crude.

The results of this testing indicate that operation on whole crude is slightly better than operation on ATB-the whole crude 3D C5+ syncrude is approximately 1.5 numbers higher in API gravity than the C5+ syncrude produced by operating the 3D unit on ATB feedstock and blending in the virgin 650F. This may be partly explained by the improvement in distillation expected from having more "front end" in the feedstock, and by the cooler regenerator temperatures.

However, subsequent operational improvements have led to the conclusion that there should be essentially no difference in product yields or quality when operating on whole crude or ATB and blending the 3D products with the virgin products for downstream processing, says Bar-co. It should be stressed that the choice of feedstock for the 3D unit is highly dependent on the final disposition of the products.

For instance, if Jet Al can be produced from the virgin crude, it may not be possible to produce Jet Al, without further hydrotreating or adjustment of the cutpoint, from the 3D unit when processing the whole crude, because of the increases in the aromatic content of that particular cut.

If the virgin 650- F. does not need to be separated from the 3D products, then the economics and capital investment strongly favor operating the 3D unit on crude.

If it is necessary to separate the products, the 3D unit can be designed with a flash tower to separate the 650F. virgin material before 3D processing.

Because the 3D process is unique in its millisecond approach to residual oil upgrading, thermal degradation of the product is minimal and hydrogenation requirements are only marginally higher than those for virgin products from the same crude.

There was little concern regarding the hydrotreating requirements of the 3D naphtha and atmospheric gas oil because these 3D products were diluted with intermediate products from other processes and upgraded in existing refinery equipment.

The main concern was with upgrading the 3D heavy gas oil (HGO) in hydrotreaters or mild hydrocrackers.

To be certain that the hydrotreating requirements were completely understood, Criterion Catalyst Co. conducted pilot plant studies on 3D products. A general description of the 3D products, as compared to virgin products, is shown in Table 2.

Economic analysis of the 3D process indicates that it is economically viable for any crude or ATB feedstock from which one does not wish to produce a specialty bottom-of-the-barrel product, such as asphalt or premium-grade coke.

The process is especially suited for upgrading heavy crudes and tar sands bitumens, producing low-viscosity bottomless reconstituted crudes, and maximizing transportation fuels at the expense of fuel oil or coke.

The 3D process can be integrated into an existing refinery or used as a stand-alone upgrader at a wellhead facility. It can be installed in place of, or parallel to, the existing crude unit furnace to add flexibility in crude slate and to eliminate the need for the vacuum unit and vacuum resid processing.

The 3D unit can also incorporate a metals-removal system that recovers metals from the crude oil by processing the circulating solids. In some cases, Bartholic believes the 3D process can be operated without any fresh solids addition.

MSCC PROCESS RESULTS

Current suppliers of catalytic cracking technology have been stressing the need for short contact time operation, catalyst "riser slip" elimination, increased catalyst-to-oil ratios, "catalyst coolers" on residual oil operations, and reduced gas yield and catalyst consumption.

The proprietary MSCC design appears to accomplish all of these goals. Its millisecond-range contact time minimizes secondary reactions. It also results in lower regenerator temperatures, which can eliminate the need for catalyst coolers in many residual oil units.

On very heavy feeds, where there is still a need for catalyst coolers, the design will at least require less catalyst cooling, which in turn results in lower coke yield and higher liquid products yields.

Short contact time will also result in significantly greater gasoline efficiency, higher gasoline octane, and less secondary cracking, accompanied by lower total LPG and gas yields. However, there is an increase in the olefin content of the C4S, which usually results in more C4 alkylate than in pre-MSCC operation. More C4 alkylate will increase pool octane.

The millisecond system also reduces the nickel activity of the circulating catalyst, possibly making passivators unnecessary. In residual oil operations, the system can also decrease the catalyst consumption by as much ;As 50% compared to today's "state of the art" technology.

Any existing FCCU can be economically converted to MSCC technology. A recent study indicates that a 20,000 b/d FCC with a high-efficiency regenerator can be revamped for $1.5-2.0 million, with a simple payout of less than 12 months.

The MSCC unit yields were compared to yields from a conventional riser-cracking FCCU, which can be described as "early 1980s technology." The data indicate the yields shift direction, but not necessarily the magnitude expected when converting an existing FCCU to MSCC operation.

Although the unit was typically operated in complete CO combustion with 40% deasphalted oil (DAO) in the feedstock, a valid yield comparison (Table 3) was obtained at conditions possible for the conventional unit by running 20% DAO with VGO, in both cases.

COMBINED SYSTEMS

In addition to opening a ,.new era of catalytic cracking," Bartholic says the systems will have the ability to greatly improve yields of today's transportation fuels from the typical refinery at reduced operating costs.

If final gasoline product specifications require hydrotreatment of all FCC feeds, the 3D/MSCC combination is a natural. In cases where hydrotreatment is not necessary, the ability of MSCC to handle residual oil is unsurpassed, according to Bar-co.

For a refinery consisting of the 3D process for crude distillation and catalyst poison removal, followed by hydrotreaters, a reformer, the MSCC process or a hydrocracker, an alkylation unit, a gas plant, selective hydrogenation Of C4s, and in some cases, a hydrogen plant, up to 90 LV % transportation fuels can be obtained.

Copyright 1991 Oil & Gas Journal. All Rights Reserved.