Sulphur and Carbon Pollutants: Origin, Forms, Desulphurisation, and Emissions, Notas de estudo de Química

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J.C. JONES

ATMOSPHERIC POLLUTION

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J. C. Jones

Atmospheric Pollution

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Atmospheric Pollution Contents

Contents

Preface

1. Introduction: The gas laws 1.1 Introduction 1.2 The Ideal Gas Equation 1.3 The mole concept 1.4 Sample calculations 1.5 The parts per million (p.p.m.) concept 1.6 Nitrogen accompanying oxygen in combustion processes 1.7 Concluding comments 2. Sulphur pollutants 2.1 Origin of sulphur pollutants 2.2 Sulphur in fuels 2.3 Form of sulphur in fuels and the fate of the sulphur on combustion 2.4 Desulphurisation of fuels 2.5 Sulphur credits 2.6 Methods of sulphur dioxide detection 2.7 Sulphur pollution levels in various countries 2.8 Sulphur dioxide emissions from shipping 2.9 Acid rain 2.10 Acid rain in the age of greenhouse gas reductions

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Atmospheric Pollution Contents

2.11 Concluding remarks 2.12 References

3. Oxides of nitrogen 3.1. Introduction 3.2 Denitrogenation of fuels 3.3 NO (^) x mitigation during burning: the ‘low NOx burner’ 3.4 Removal of NOx from flue gas by selective catalytic reduction 3.5 NO (^) x from vehicles 3.6 NO (^) x from shipping 3.7 NO (^) x credits 3.8 Means of measuring NOx 3.9 Concluding numerical exercise 3.10 References 4. Particulate 4.1 General introduction 4.2 PM (^10) 4.3 PM (^) 2. 4.4 Smaller particles than PM2. 4.4 Concluding comments 4.5 References 5. Volatile organic compounds (VOC) and ozone 5.1 Introduction

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Atmospheric Pollution Contents

8. Chlorinated pollutants 8.1 Hydrogen chloride 8.2 Chlorofluorocarbons (CFCs). 8.3 Elemental chlorine 8.4 Dioxins 8.5 References 9. Greenhouse gases Part I: Background 9.1 Introduction to the greenhouse gas chapters 9.2 Gas radiation 9.3 Why ‘greenhouse’? 9.4 A simplified model for the emissivity of the troposphere 9.5 Levels of carbon dioxide in the atmosphere 9.6 The distinction between fossil fuel and non-fossil fuel carbon dioxide 9.7 Carbon dioxide emissions from natural gas and petroleum fuels 9.8 Methane as a greenhouse gas 9.9 Sources of carbon dioxide other than fossil fuel combustion 9.10 References 10. Greenhouse gases Part II: Mitigation measures, emission targets and carbon trading 10.1 Introduction 10.2 Reduction of carbon dioxide emissions from power generation 10.3 Carbon credits 10.4 Carbon dioxide from vehicles

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Atmospheric Pollution Contents

10.5 Carbon dioxide from aircraft 10.6 Carbon dioxide from shipping 10.7 Miscellaneous sources of carbon dioxide 10.8 Uptake of carbon dioxide by vegetation 10.9 Carbon dioxide sequestration 10.10 Concluding remarks 10.11 References

11. Radioactivity in the atmosphere 11.1 Radon 11.2 Uranium 11.3 Thorium 11.4 Polonium 11.5 Cosmic rays 11.6 Carbon- 11.7 Iodine 11.8 Caesium 11.9 Some nuclear incidents 11.10 References

Postscript

Notes

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Atmospheric Pollution Introduction: The gas laws

1. Introduction: The gas laws

1.1 Introduction

Air is a gaseous substance, so an understanding of its behaviour requires knowledge of what are known as the gas laws. That is the purpose of this preliminary chapter.

1.2 The Ideal Gas Equation

This is:

PV = nRT

where P = pressure (N m-2^ ), V = volume (m^3 ), n = quantity in moles (see below), T = temperature (K), R = gas constant = 8.314 J mol-1^ K-^.

1.3 The mole concept

The following should be carefully noted.

(a) Quantity in moles = quantity in grams/molar weight in grams per mole

(b) molar weight in grams per mole numerically equal to the molecular weight.

(c) One mole of any substance contains 6.02 u 10 23 molecules. This is the Avogadro number, symbol No , units mol-^.

(d) molar weight (g mol-1^ ) = weight of one molecule (g) u No (mol -1^ )

(e) It follows from the ideal gas equation that a cubic metre of any gas, gas mixture, vapour or gas-vapour mixture at 1 bar pressure and room temperature contains approximately 40 moles. In calculations appertaining to air quality, for temperatures in the range say 10 to 30o^ C to use a value of 40 moles is acceptable. There is no need to do an ideal gas calculation to refine the value.

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Atmospheric Pollution Introduction: The gas laws

1.4 Sample calculations

The examples below illustrate some if these ideas.

Question:

How many moles and how many molecules are there in 35 g of nitrogen (N 2 )? At 25 oC (= 298K) and 1 bar (10 5 N m -2) pressure, what volume would this quantity of nitrogen occupy?

Answer:

Atomic weight of nitrogen = 14, therefore molecular weight of nitrogen gas = 28. So number of moles = 35/28 = 1.25.

Number of molecules = 1.25 N (^) o = 7.53 u 10 23

Using the ideal gas equation:

V = nRT/P = [1.25 u 8.314 u 298/(1 u 105 )] m 3 = 0.031 m 3 (31 litre)

Alternatively, 1.25 mol/40 mol m -3^ = 0.031 m 3

1.5 The parts per million (p.p.m.) concept

Parts per million is analogous to percentage, which is of course parts per hundred, hence: p.p.m. = (moles of gas of interest/total moles) u 10 6

A related calculation follows.

Question:

At a particular place, the air standard for sulphur dioxide as an annual average is 90 Pg m-3^ at 25 oC. Re-express this in p.p.m. Molar mass of sulphur dioxide = 64 g.

Solution:

90 Pg { 90 u 10 -6/64 mol in a total of 40 mol gas, therefore:

p.p.m. SO 2 = {90 u 10 -6/64]/40} u 10 6 = 0.035 p.p.m.

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Atmospheric Pollution Sulphur pollutants

2. Sulphur pollutants

2.1 Origin of sulphur pollutants

The primary origin is sulphur in fuels. When such fuels are burnt the sulphur goes to sulphur dioxide, which is harmful to humans and to vegetation as well as being a contributor to acid rain. We live in an age in which oil prices influence the world economy strongly and, at times, critically. It is because of the difficulty with sulphur that the sulphur content of a particular crude oil is a factor in its pricing, as will be explained more fully below.

2.2 Sulphur in fuels

When a crude oil is refined the sulphur within it is distributed across the fractions, tending to be more concentrated in the higher boiling fractions. In subsequent burning the sulphur will be converted to sulphur dioxide. That is why crudes are sometimes desulphurised which, of course, involves processing expenses. Benchmark crudes specify a maximum sulphur content which, if exceeded by an actual crude, will attract a reduction in price. As examples Brent crude, the North Sea benchmark, contains up to 0.37% sulphur and the West Texas Intermediate (WTI) benchmark up to 0.24%. Table 2.1 below gives some examples of sulphur contents of eleven selected crudes. In each case the sulphur content should be seen as no more than that of a representative sample having been determined by an approved standard.

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Atmospheric Pollution Sulphur pollutants

Table 2. Sulphur in selected examples of crude oil.

Name of the field and location

Operator of the field Sulphur content %

Alba field, North Sea, British sector

Chevron Texaco 1.

Burgan Field, Kuwait Kuwait Oil Company 1. Fateh Field, Dubai Dubai Petroleum Company 2. Lufeng field, South China Sea

Statoil 0.

Minas Field, Indonesia Chevron 0. Morpeth Field, Gulf of Mexico Eni Oil Company 1. Oregano Field, Gulf of Mexico

Shell 1.

Pluntonio Field, Angola. BP 0. Statfjord Field, North Sea, Norwegian sector

Statoil 0.

Tapis Field, Malaysia Petronas and Esso 0. White Rose Field, eastern Canada

Husky Energy 0.

Average over world oil fields in operation

Considering in broad terms two of the OPEC countries, Venezuelan crudes tend to be high in sulphur and Nigerian crudes low in sulphur. Liquid fuels made from shale tend to be higher in sulphur than their counterparts from crude oil. Some examples of natural gas, as it emerges from a well, contain only traces of sulphur. There are however many examples of ‘sour’ natural gas, that is, natural gas containing large amounts of sulphur in the form of hydrogen sulphide H 2 S.

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Atmospheric Pollution Sulphur pollutants

Table 2. Desulphurisation operations at selected refineries.

Refinery details Desulphurisation activity Antwerp Refinery (Operator Esso. Capacity | 250000 barrels per day)

Removal of sulphur from FCC gasoline by hydrogen treatment introduced in 2005.

Ruwais Refinery, UAE (Operator Abu Dhabi Oil Refining Company a.k.a. Takreer. Capacity 120000 barrels per day)

Hydrotreatment in the presence of a Co/Mo catalyst to remove sulphur from the diesel fraction.

Luena Refinery, Germany. (Operator Total. Capacity 200000 barrels per day)

Removal of sulphur from some of the incoming crude. Port Jérome-Gravenchon Refinery, France (Operator Esso. Capacity | 250000 barrels per day)

Desulphurisation unit of capacity 48000 barrels per day for transport fuels.

Szazhalombatta Refinery, Hungary (Operator Magyar Olaj- és Gázipari Nyrt, a.k.a. MOL. Capacity 161000 barrels per day)

Diesel desulphurisation using a novel catalyst.

Thessaloniki Refinery, Greece. (Operator Hellenic Petroleum. Capacity 67000 barrels per day)

A new desulphurisation facility to enter service in 2009.

Mongstad Refinery, Norway (Operator Statoil. Capacity 200,000 barrels per day)

Transport fuels with 10 p.p.m. of sulphur produced.

Edmonton Refinery, Canada (Operator Petro- Canada. Capacity 190000 barrels per day)

Upgrading of the desulphurisation plant to meet Canadian Federal requirements for sulphur content of transport fuels.

Referring to the first row, concerned with the Antwerp refinery, the term FCC denotes fluid catalytic cracked gasoline. This is material initially higher boiling than gasoline, brought into the gasoline boiling range by the cracking process. Where FCC material is present in a gasoline having been blended with straight-run material it contributes by far the greater part of the total sulphur present. The method used at Antwerp is known as the Axens Prime G+ process and is also taking place in refineries in countries including Canada and the US to produce ‘ultra-low sulphur’ automotive fuels [1]. At the Ruwais refinery diesel having been catalytically hydrotreated as described in the table is blended with diesel not having been so treated, to give an acceptably low sulphur content of the final product. At the Leuna refinery sour crude is desulphurised, and an important product is low-sulphur distillate oil for heating. The capacity of this unit is just under a tenth that of the refinery itself. The desulphurisation plant at the Port

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Atmospheric Pollution Sulphur pollutants

Jérome-Gravenchon refinery is a Gofiner Unit, itself an Exxon Mobil technology. A Gofiner Unit combines desuplhurisation with other functions including cracking, enabling heavy material would otherwise have formed part of the residue to become a blendstock for distillate products.

The Szazhalombatta refinery uses a catalyst developed by Haldo Topsoe in Denmark which can be used with existing hydrotreating facilities, leading to diesel product as low as 5 p.p.m. in sulphur. The upgrade at the Thessaloniki Refinery was necessitated by Greece’s entry to the EU in 2001 and the duty consequently incumbent upon her to supply fuels conforming to EU specifications. This is a fairly small refinery in terms of its capacity, and there are plans to raise this to about 90000 barrels per day. The desulphurisation plant at the Mongstad Refinery came into operation in 2003. Working for convenience in UK currency, its use added about 1.2 p to the cost of a litre of gasoline from the refinery at a time when gasoline sold in the UK for somewhat less than £1 (100p) per litre. What distinguishes the Edmonton refinery in the last row from the other seven in the table is that it receives not crude oil in the conventional sense but bitumen from tar sands.

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Atmospheric Pollution Sulphur pollutants

2.5.2 Related calculations.

Such calculations are in the shaded areas below and are interspersed with comments.

Imagine heat supplied by the combustion of heavy residual fuel oil. The calorific value of such a fuel will be | 44 MJ kg -1. A quantity of 2 GJ (2000 MJ) of heat will be produced by burning:

(2000/44) kg = 45 kg

Let the percentage sulphur in the fuel oil = x. If the emission standard above of 1 kg of sulphur dioxide per 2 GJ of heat is to be precisely met:

45 u ( x /100) u 2 = 1

where the factor of 2 arises from the fact that the molecular weight of SO 2 is twice the atomic weight of sulphur

x = 1.1%

This then is the maximum sulphur content of fuel oil that could be used without exceeding the standard. The calculation continues below.

Imagine that the fuel oil previously described is used to raise steam for electricity generation at 500 MW using a turbine operating on a Rankine cycle of 35% efficiency. The quantity of sulphur dioxide from a day’s operation of the turbine will be:

(500 u 10 6 /0.35) J s -1^ u (24 u 3600) s u 10 -9^ GJ J -1^ u 0.5 kg GJ -1^ u 10 -3^ tonne kg -

= 62 tonne

The above figure represents operation of the turbine at the very limit of its sulphur dioxide allowance. In the following we consider:

Financial penalties if a fuel oil of 20% higher sulphur content was used and

Financial benefits if a fuel oil of 20% lower sulphur content was used.

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Atmospheric Pollution Sulphur pollutants

20% higher sulphur content gives 1.32% sulphur. Sulphur dioxide released in a day given by:

[(500 u 10 6 /0.35) J s-1^ /44u 10 6 J kg -1^ ] u(24 u 3600) s u 10 -3^ tonne kg -1^ u(1.32/100)u 2

= 74 tonne

20% lower sulphur content gives 0.88% sulphur. Sulphur dioxide released in a day given by:

[(500 u 10 6 /0.35) J s -1^ /44u 10 6 J kg -1^ ] u(24 u 3600) s u 10 -3^ tonne kg -1u (0.88/100) u 2

= 50 tonne

The fuel oil of higher sulphur content would necessitate purchase of sulphur credits of 12 tonne per day, whilst that of lower sulphur content would free up sulphur credits to the same extent. In either case, whether money was being paid or received, the sum would be something in the region of $US25000 per day.

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