DANUBE REFINERY OPERATES UNDER COMPLEX AIR REGULATIONS

May 30, 1994
L.R. Aalund Managing Editor-Technology A good example of a major refinery coping with German environmental regulations is the Erdocl-Raffinerie Neustadt GmbH & Co. (ERN) refinery near the town of Neustadt a.d. Donau, or Neustadt on the Danube, in lower Bavaria. ERN is a joint venture of Mobil Oil AG,, and Ruhr Oel GmbH. Ruhr Oel is in turn a joint venture of Petroleos de Venezuela S.A. and Veba Oel AG. Veba operates the refinery.
L.R. Aalund
Managing Editor-Technology

A good example of a major refinery coping with German environmental regulations is the Erdocl-Raffinerie Neustadt GmbH & Co. (ERN) refinery near the town of Neustadt a.d. Donau, or Neustadt on the Danube, in lower Bavaria.

ERN is a joint venture of Mobil Oil AG,, and Ruhr Oel GmbH. Ruhr Oel is in turn a joint venture of Petroleos de Venezuela S.A. and Veba Oel AG. Veba operates the refinery.

The 7 million tons/year (144,000 b/d) complex refinery deals regularly with nearly 30 different crude oils, arriving via the Italian port of Trieste and the Trans Alpine Line from the Middle East, North and West Africa,

Venezuela, and the North Sea. Table 1 is a listing of these crudes and some of their characteristics that are important in the refinery's environmental program.

The refinery started up in 1964 with one crude oil distillation unit and was expanded with a second one in 1972. Vacuum distillation capacity now totals 2.4 million tons/year (65,000 b/cd). The refinery also has a visbreaker, two catalytic reformers, naphtha and gas oil desulfurizers, and a 1.5 million tons/year (26,000 b/cd) fluid catalytic cracker.

Typical yields of major products are: LP-gas and refinery gas, naphtha and gasoline, 30.6%; middle distillate, 46.3%; heavy fuel oil, 9.8% and asphalt, 3.7%.

An indication of the changing times is that 25% of the refinery's output in 1973 was heavy fuel oil, compared to less than 10% today.

Some 47% of the refinery's output is shipped by tanker truck, 43% by rail. In addition, the refinery pipes naphtha, LPG, and refinery gas to a nearby steam cracker.

ERN is not the only refinery in the region north of Munich. There is 215,000 b/cd of capacity in two refineries about 20 miles away at Vohburg and Ingolstadt, which is also the home of an Audi automobile plant.

But ERN is in a relatively isolated pastoral setting of fields and forests about 1 1/2 miles south of the Danube (see cover). Hops which go into the world famous Bavarian beers are a major crop in the region and the refinery is only 2 miles from a spa popular since the Romans occupied the Danube valley. German physicians still send patients there to relax, drink the waters, and breathe the country air for a variety of ailments.

In short, ERN is in a high-profile setting that demands maximum attention be paid to environmental matters.

AIR

Although there has been a series of German air pollution control laws since well before the turn of the century, all current regulations flow from the Bundes-immissionsschutzgesetz, or Federal Immissions Control Act, of 1985. It is equivalent to the U.S. Clean Air Act in its scope. It is of interest to note that the German language and regulations make a distinction between "immissions" and "emissions," similar to the distinction between immigrants and emigrants. Emissions are potentially harmful substances, including noise, that a source emits, while immissions are what flora and fauna and the environment receive.

German refiners must deal with two sets of air quality control regulations that stem from the act. They are:

  • The Ordinance on Large Combustion Plants (Grossfuerungsanla-gen-Verordnung)

  • Technical Instructions on Air Quality Control (TA-Luft or Anleitung zur Reinhaltunc, der Luft)

Inspections are performed by federal factory inspectorates and independent institutions, while monitoring and enforcement are done by environmental authorities of the various federal states or Lander.

LARGE COMBUSTION PLANTS

The ordinance covering emissions from large combustion plants (LCPO's) was basically written for electrical-generating stations, generally firing one fuel and often coal. One aim of the ordinance was to keep low-sulfur fuel for smaller plants and to get the high-sulfur fuel into the larger plants, where stack gas clean up is mandatory. The regulation has been tweaked a bit to make it more suitable for refineries which get a great deal of their energy from gases produced during processing and often mix gaseous and liquid fuels.

But a major unit in the refining industry, the fluid catalytic cracking unit (FCCU), does not come under the LCPO. It is under TA-Luft.

Table 2 shows emission limits for existing refineries (and power plants) ranging in size from less than 100 mw to greater than 300 mw. Plants as large as 300 mw can stay within the 1,700 mg/cu m limit by burning 1% sulfur fuel oil. The concentration limit drops dramatically for plants larger than 300 mw, and they must employ stack gas cleanup if burning heavy fuel oil and reach a sulfur removal efficiency of 85%.

However, the ERN refinery, which is rated as a 300 mw facility, is working under a so-called " bubble" as a result of an agreement with Bavarian authorities.

Generally said, a bubble means the refinery is figuratively under a dome or bubble and the limits for SO2 and NOx apply to what is released from this bubble, not the individual sources or units under it.

This agreement limits emissions of SO2 from the bubble to 3,250 tons /year in 1994, the same as in 1993, but well down from the 4,000 tons allowed in 1991 and the 5,000 tons allowed in 1988.

The NOx limit from heaters and the FCCU regenerator is 1,100 tons/year.

Carbon monoxide and particulates do not come under the bubble arrangement. As Table 2 shows, there are different limits when firing gas, which is sulfur-free, and liquid fuels. ERN fires a mixture of heavy fuel oil, refinery gas, and natural gas, as Fig. 1 shows. ft has been burning natural gas to limit NOx since beginning the export of refinery gas to the petrochemical complex.

Fig. 1 also shows there are two Claus sulfur recovery units. They have a total capacity of 40 tons/year. The offgas from Claus unit No. 2 is not analyzed.

The SO2 to the stack from this unit is back-calculated using produced sulfur and a Claus unit efficiency of 98%. The results are added to the bubble output. The Claus No. 1 offgas, as Fig. 1 shows, is, analyzed.

Carbon dioxide and particulates emissions must fall under specific but varying limits depending on whether the fuel is gas or liquid. ERN's regulatory limits for particulates are 5 mg/cu m when burning totally gas and 50 mg/cu m when burning totally fuel oil. Its CO limits are, respectively, 100 and 175 mg/cu m.

Of the total fuel burned at ERN, 30-40% is heavy fuel oil, the remainder natural gas and refinery gas. In such a case, the refinery is allowed to ratio or weight the limits for carbon monoxide and particulates emission limits depending on the amount of each fuel burned.

However, if the amount of heavy fuel oil reaches 50%, then ratioing isn't allowed and the heavy fuel oil limits of 175 mg/cu m CO and 50 mg/cu m particulates take effect. It can weight the limits at five out of the six measurement stations (designated with "Q" in Fig. 1).

These five come under the Large Combustion Plant regulation and include the reformer furnaces now burning only gas but which are capable of burning fuel oil.

The CO boiler and FCC regenerator come under the TA-Luft air regulation, which sets the limits from the fluid catalytic cracker's regenerator and CO boiler at 50 mg/cu m particulates and 100 mg/cu m CO.

OTHER COMPOUNDS

The particulate regulations also address the content of metallic compounds in the offgas. Arsenic, lead, cadmium, chrome, cobalt, nickel, and their compounds may not, expressed in elemental form, exceed together 2 mg/cu m in the flue gas. Cadmium, lead, and chrome are negligible in the residue.

Cobalt and arsenic contents are about 4 mg/kg.

Although the other metals are present in the heavy fuel, the main issue is nickel. To meet the nickel limit, the vacuum residue should not contain more than 24 mg/kg or 40 ppm nickel (Table 1).

Because the fuel gases do not contain metals, the restrictions are met by ratioing gas and fuel oil to meet the 2 mg/cu m limit.

Gas firing dilutes the concentration of nickel in the flue gas.

However as Table 1 shows, some relatively good crudes, including Nigerian streams, have to be avoided at times because of their nickel content.

The refinery segregates residue material to make 24 ppm nickel fuel oil and a second grade containing as much as 48 ppm nickel.

The latter is exported to areas outside of Germany where there is no nickel limit, The refinery fuel is a blend of visbreaker resid and FCC slurry oil.

MORE AIR REGS

The FCC regenerator, as mentioned previously, also contributes emissions. This brings the"TA-Luft" or Technical Instructions on Air Quality Control into play.

The waste gas from units covered by this regulation may not exceed the following mass concentration when the catalyst is regenerated: particulates, 50 mg/cu m; nitrogen oxides indicated as nitrogen dioxide, 700 mg/cu m; and sulfur oxides indicated as sulfur dioxides, 1,700 mg/cu m.

The volume of the regenerator offgas, which is continuously monitored at ERN, runs about 65,000 cu m/hr. Although the SOx and NOx have limiting concentration values, the mass output of each is debited against the yearly bubble limit.

The TA-Luft regulations do not address fugitive emissions from valves, flanges, and pumps directly, but do give the state and technical agencies the authority to precisely specify the type of equipment and its design for use in specific services, defined, for example, by vapor pressure, content of carcinogens, or toxic materials. They do diligently, exercise this authority.

Vapor recovery is closely controlled. Gasoline loading at the refiner-v's tank car and rail loading racks are done under suction and the vapor is routed to a McGill vapor recovery unit (VRU) that employs active carbon adsorption.

The unit is doing an excellent job, according to Horst Gobel, the refinery director.

The VRU at ERN keeps benzene in the clean gas at less than 0.1 mg/cu m, compared to a limit of 130 mg/cu m, and total hydrocarbons at 8 mg/cu m, compared to a limit of 130 mg/cu m. There are, at times during loading, peaks in the total hydrocarbon concentration of about 60 mg/cu m in the clean gas.

Also under TA-Luft are the two sulfur recovery plants with a total capacity of 15,000 ton /year or 40 ton/day. At present the ERN refinery is producing 20 ton/day sulfur and must operate the sulfur plants at 98% efficiency. This requires the use of Lurgi Sulfreen tail gas units.

Should sulfur production exceed 50 ton/day, the unit must operate at 99.5% efficiency. When the sulfur content of light heating oils is reduced to 0.05 wt %, as it is expected to be in 1995, Gobel says the Claus unit efficiency will have to be increased by installing an additional Carbo-Sulfreen tail gas stage.

FCC LINES

As at most refineries, FCC catalyst fines demand special treatment. As Fig. 1 shows, the FCC unit has its own set of analyzers because of the different regulatory niche it occupies and because of its catalyst fines emissions. The regulations for the FCC call for particulate limits of 50 mg/cu m.

To accomplish this, ERN employs a third-stage Polytrol separator and an electrostatic precipatator (ESP). The Polytrol unit employs a large number of small cyclones in series. This unit opens the door to incorporation of an expander in the system.

The four-cell Research Cottrell ESP, which is placed after the CO boiler, permits reduction of catalyst fines down to a level of 35-45 mg/cu m (Fig. 2).

ANALYSIS

There are six sets of analyzers in the ERN flue gas-monitoring system, all designated, as mentioned earlier, with "Q" on Fig. 1.

One type of analyzer employs nondispersive infrared for measurement and can analyze for either NOx, SO2, or CO.

However, one analyzer is dedicated to each of these compounds, which means there are 17 analyzers of this tv e in the system (no CO is measured in the FCC offgas).

The particulate analyzer on the reformers is not in use because gas is now being burned there, as shown in Fig. 1.

The types and brands of analyzers are specified by the authorities.

There are six oxygen analyzers in the flue gas system. They use a magnetic principles The oxygen analysis is important because all limits and amounts are calculated on the basis of 3% oxygen in the flue gas, so the actual amount must be known.

There also are six optical particulate analyzers, one in each of the five ducts from heaters to the stacks and another in the regenerator offgas duct.

Only the particulate analyzers are located in the duct. Flue gas samples are drawn out of the ducts through small lines for the other analyzers, which are in analysis rooms near the base of the stacks. Fig. 3 shows one of the four analysis rooms, which also serves the FCC unit, at the base of Stack 4.

An analysis system (Fig. 4) is shown in this house with dedicated analyzers for, from top to bottom, O2, NO, CO, and SO2. The regulations require an automatic calibration with certified test gas each week for these analyzers.

SO2 and particulate analyses are not required when the flue gas comes totally from gaseous fuels as is the case for the catalytic reformer.

A report is filed to the authorities each month; earlier if a major deviation occurs. The authorities also have the option to visit the plant and inspect the analyzer results and operations any time they desire. ERN also uses the analytical results for process and operational information. Fig. 5 shows the dedicated bank of printers.

The analytical systems with computers cost nearly 52 million, Gobel estimates. Running and maintaining them costs an estimated $200,000/year.

RECORDING

Fig. 6a is an example of the printouts, which are formatted for the authorities, of analyses for flue gas to Stack 1 from the heaters for visbreaker and crude oil distillation unit No. 1 (Fig. 1). The flue gas from the heater for the vacuum distillation unit is not analyzed because the heater is fired with gas.

Fig. 6b is an example of a printout covering the flue gas from the FCC regenerator.

The fact that the flue gas to Stack 1 in Fig. 6a is governed by the Large Combusion Plant regulation, while that from the FCC regenerator is governed by air quality regulation (TA-Luft), is reflected in the information on the printouts. This is described more fully in notes on the figure.

Fig. 6a has all the information necessary to calculate the mass of sulfur emitted from Stack 1 except for the volume of flue gas. The fired duty contributed by either gas or oil in each heater is shown in megawatts because:

  • Emissions are based on the Large Combustion Plant regulation which is governed by the total megawatts of fired duty in the refinery.

  • Allowable CO and particulate concentrations, as mentioned earlier, depend on the ratio of oil burned to gas.

  • For converting megawatts to flue gas volume in order to calculate the mass Of SO2 emitted to the bubble, 1 mw of oil firing is considered equivalent to 1,016 cu m/hr of flue gas; 1 mw of gas is equivalent to 954 cu m/hr.

Fig. 6b has no megawatt values because this is not a factor in the TA-Luft regulation (only concentration is important). But because ERN is under a bubble, the mass of SO2 emitted must be calculated and the offgas volume (E3M3/H, or 1,000 cu m/hr) is given.

The emission measurements also are used by the operators to recognize trends. If the trend is to exceed a limit, the emissions are brought in line by burning less heavy fuel oil.

INDUSTRIAL NOISE

The noise from the refinery cannot exceed 40 db(a) at a distance of 800 m (875 yards). That is equivalent to the sound level of light music. Ironically, it is not possible to measure it because of traffic noise, so ERN hires a consultant to measure the levels inside the refinery and calculate what the sound power level would be for the control vacinity.

ERN has spent a great deal of money over the past years to meet these limits. The refinery has isolated its wall-fired furnaces and utilizes bottom firing in new or replacement furnaces to reduce noise emissions. It also has enclosed such equipment as compressors and turbines.

The sound power level is an important specification when ordering new equipment. "In former times," Gobel says, "it was difficult to carry on conversations in the plant. Now there is no problem, even near the furnaces."

WATER

ERN employs a traditional water treatment system with oil separation and flotation steps followed by a two-train biological system, each train currently handling 45 cu m/hr or about 120 gal/hr (240 gal/hr for both). The limit for water effluent is 350 cu m/hr during dry weather.

Table 3 shows the limits and sample location. A yearly report covering the monitoring and analyses must be filed with the state water authorities.

Copyright 1994 Oil & Gas Journal. All Rights Reserved.