Cover Image
close this bookEnvironmental Handbook Volume II: Agriculture, Mining/Energy, Trade/Industry (GTZ, 1995, 736 p.)
close this folderMining and energy
close this folder41. Thermal power stations
View the document1. Scope
View the document2. Environmental impacts and protective measures
View the document3. Notes on the analysis and evaluation of environmental impacts
View the document4. Interaction with other sectors
View the document5. Summary assessment of environmental relevance
View the document6. References
View the document7. Appendices

7. Appendices

A-1 Flow diagram of energetically and environmentally relevant materials in a thermal power plant
A-2 Schematic diagram of a thermal power plant equipped with various flue-gas cleaning systems
A-3 Details of various desulfurization processes
A-4 Immission limits standards as per the German TA-Luft
A-5 German laws and regulations governing the limitation of emissions from thermal power plants
A-6 Emission limits for air pollutants from large firing installations (³ 50 MW) in Germany; emission limits for new, large-scale, coal-fired power plants in various countries, plus pertinent EC and World Bank standards; conversion chart for SO2 and NOx emissions
A-7 Minimum requirements as per German Federal Water Act (WHG) section 7a
Appendix 47: Scrubbing of flue gases from combustion plant, Sept. 8, 1989

Appendix A-1 - Flow diagram of energetically and environmentally relevant materials in a thermal power plant


Flow diagram of energetically and environmentally relevant materials in a thermal power plant

Appendix A-2 - Schematic diagram of a thermal power plant equipped with various flue-gas cleaning systems


Schematic diagram of a thermal power plant equipped with various flue-gas cleaning systems

Appendix A-3 - Details of various desulfurization processes

In-boiler desulfurization techniques are employed for solid fuels, e.g., in fluidized-bed combustion systems. The SO2 forming in the flue gas combines with lime or limestone injected into the combustion system. Desulfurization therefore takes place simultaneously with fuel combustion at roughly 850°C. That relatively low combustion temperature helps limit NOx emissions to 200 - 400 mg/m³STP. The degree of desulfurization ranges between 80 % and 90 %. Fluidized-bed combustion systems, which only can be used in new power plants, operate according to either the stationary or the circulating principle, with the latter achieving the lower emission levels under otherwise identical boundary conditions.

Dry additive processes can be applied to coal-fueled, grate- and dust-fired boilers. At a temperature below 1000°C, a pulverized lime product, e.g., slaked lime, is injected into the flue gas at a point above the combustion chamber, where it reacts with the SO2 and precipitates. The requisite equipment is retrofittable and can remove 60 - 80 % of the sulfur from the flue gas.

The residual product from fluidized-bed combustion and dry additive processes - a mixture of coal ash, CaO or other unreacted additive, and various calcium salts (CdSO4, CaCl2, CaF2) - is separated out in a downstream dust precipitator. In each case, it should be ascertained whether or not the residue can be put to some practical use, perhaps in the building materials industry (usually somewhat problematic due to the mixed salts), or will instead require safe disposal.

There are three basic types of flue-gas desulfurization processes:

- wet processes
- spray-dryer processes
- dry processes.

The wet process using limestone, lime or slaked lime as the additive and producing gypsum as a reaction product is the most widely employed commercial-scale alternative. It has yielded the largest worldwide empirical potential and is used in the majority of facilities. Appropriately processed via drying and pelletizing, for example, the gypsum can be used by the building materials industry, mixed with fly ash and landfilled, or used for land reclamation purposes in coastal areas (cf. section 2.5).

In the spray-dryer process, the sorbent (lime or slaked lime) is sprayed as an aqueous solution into an absorber at 60 - 70°C. As the water introduced with the suspension evaporates, the additive reacts with any SO2 present to produce a fine-grained reaction mixture that precipitates out in downstream particulate removal equipment. Consisting of various calcium salts (CaSO4, CaSO3, CaCl2, CaF), excess sorbent and residual fly ash, the reaction product can either be landfilled or used for land reclamation purposes. Potential preteatment requirements for the residue and additional measures for preventing groundwater or coastal-water contamination due to leaching are dealt with in section 2.5.

Other flue-gas desulfurization techniques, most notably dry processes using activated charcoal and regenerative processes involving sodium sulfite as the sorbent and sulfur dioxide as an intermediate product capable of further processing into sulfuric acid or sulfur, have become widely accepted in some areas and can be used for various other specific situations. As a rule, however, such processes are more elaborate and expensive than the limestone/gypsum techniques, and they impose particularly stringent standards on the quality of the end products, for which a corresponding market, e.g., the chemical industry, is needed.

Assuming otherwise identical constraints, the quantities of residue produced derive in descending order from the dry sorbent, spray drying, scrubbing with gypsum, and scrubbing with sulfuric acid or sulfur (cf. section 2.3).

Appendix A-4 - Immission limits as per the German TA-Luft

Pollutant



IW 1

IW 2

-

Suspended particles

mg/m³


0.15

0.30

-

Lead and inorganic lead compounds as components of the suspended particles indicated as Pb

µg/m³


2.0

-

-

Cadmium and inorganic cadmium compounds and components of the suspended particles indicated as Cd

µg/m³


0.04

-

-

Hydrochloric acid indicated as Cl

mg/m³


0.10

0.20

-

Carbon monoxide

mg/m³


10.0

30.0

-

Sulfur dioxide

mg/m³


0.14

0.40

-

Nitrogen

mg/m³


0.08

0.20

The above table lists the immission limits for the prevention of health hazards as prescribed by the German TA-Luft, (Technical Instructions on Air Quality Control). The values IW1 and IW2 are the short-term and long-term limits, respectively. In assessing the environmental compatibility of a thermal power plant, its IW2-value (continuous operation), for which TA-Luft specifies a monitoring period of one year, is significant.

As protection against substantial detriment and nuisance attributable to particulate precipitation, TA-Luft prescribes the following limits referred to as deposition values.

Pollutant

IW 1

IW 2

Particulate deposition

g/(m²d)

0.35

0.65

Lead

mg/(m²d)

0.25

-

Cadmium

µg/(m²d)

5.0

-

Thallium

µg/(m²d)

10.0

-

Fluorine

µg/(m²d)

1.0

3.0

The inorganic compounds in the above table are regarded as particulate constituents, with fluorine HF and the inorganic gaseous fluorine compounds counting as F.

Relatively little information is available on the combined, so-called synergistic, effects of pollution and on the interaction of atmospheric pollutants.

The toxicological effects of the various pollutants are listed in the Compendium of Environmental Standards.

The main effects of the most important pollutants are essentially as follows:

- Lead inhibits various globular metabolic enzymes in humans and other mammals, causing disruption of the oxygen balance and tidal volume. Sustained intake of less than 1 mg Pb/d has injurious effects. For plants, which take in lead primarily from the soil as opposed to the air, lead is only mildly toxic, the tendency being to lower the quality, but not the quantity, of the produce.
- Cadmium, a freely soluble metallic element, is resorbed into the digestive tract and stored in the liver and kidneys of humans and other mammals. Like its various compounds, cadmium has carcinogenic properties. In Asia, the so-called Itai-Itai and Aua-Aua syndromes were found to have been caused by Cd-polluted rice. Even low concentrations of cadmium in the soil can cause extensive damage to plants. Plants assimilate cadmium through their roots as well as their leaves and branches. Apart from reducing yields, cadmium contamination is hazardous to human health in that it enters the food chain as a cumulative toxin.
- Carbon monoxide, with its affinity for hemoglobin, the protein pigment responsible for the transport of oxygen, is toxic to humans and other vertebrates. Ingested exclusively by inhalation, carbon monoxide is odorless, colorless, tasteless and otherwise imperceptible to the senses. CO is nontoxic to plants, because it rapidly oxidizes to form CO2, which plants need for photosynthesis.
- Sulfur dioxide causes corneal clouding, respiratory distress, inflammation of the respiratory tract, irritation of the eyes, disorientation, pulmonary edema, bronchitis and cardiovascular insufficiency in humans and other mammals.

Sulfur dioxide exposure causes both direct damage to the aboveground parts of plants and indirect damage primarily by way of soil acidification.

- Nitrogen oxides resulting from combustion processes occur in the atmosphere mainly as nitrogen monoxide NO and nitrogen dioxide NO2. The preferred generic term is nitrous gases (NOx)

Inhaled by a human or animal, an NOx gas enters the lungs and irritates the mucous membranes. While NO2 leads to pulmonary edema, NO affects the central nervous system.

In a photochemical smog situation, nitrogen oxides and hydrocarbons combine to form nitrate compounds that cause irritation of the eyes and mucous membranes.

All nitrous gases are toxic to plants, as evidenced by brown to brownish-black leaf margins and spots. The poisoning process culminates in dry withering of the damaged cells.

Compared to nitrogen monoxide NO, nitrogen dioxide NO2 is substantially more toxic. For plants and animals, NO2 is less hazardous than for human beings. Atmospheric NO oxidizes to NO2; consequently, NO is prevalent in the near vicinity of combustion plants and is gradually supplanted by NO2 with increasing distance from the source.

Appendix A-5 - German laws and regulations governing the limitation of emissions from thermal power plants

- Federal Immission Control Act (Bundes-Immissionsschutzgesetz) (BImSchG)

· Ordinance on Large Firing Installations (Groeuerungsanlagenverordnung) (GFAVO)
· Technical Instructions on Air Quality Control (Technische Anleitung zur Reinhaltung der Luft) (TA-Luft)
· Technical Instructions on Noise Abatement (Technische Anleitung zum Schutz gegen L) (TA-L)
· Hazardous Incident Ordinance (Stllverordnung)

- Resolution of the Conference of Ministers for the Environment concerning mandatory dynamization of the Ordinance on Large Firing Installations with regard to nitrogen oxide emissions (Beschluder Umweltministerkonferenz) (UMK)
- Federal Water Act (Wasserhaushaltsgesetz) (WHG)

· General Administrative Framework Regulations on... Wastewater (Rahmen-Abwasser-Verwaltungsvorschrift), Annexes 31, 47 to section 7a (AbWVwV)
· Provisions governing the handling of substances constituting a hazard to water (section 199) (AbWVwV)

- Ordinance on the industrial sources of wastewater (Abwasserherkunftsverordnung) (AbWHerkV)
- Waste Avoidance and Waste Management Act (Abfallgesetz) (AbfG)

· Technical Instructions on the storage, chemical, physical and biological treatment, incineration and storage of waste requiring particular supervision (TA-Abfall)

Appendix A-6 - Emission limits for air pollutants from large firing

Installations (³ 50 MW) in Germany



Data stated in mg/m³STP, dry base











Type of fuel

MW*

Dust


Nox (as NO2)

SOx (as SO2)

CO

HCl

HF






Solid

£ 300 >300

50 50


400 200

2000 (400)1) 400

250 250

200 100

30 15






Liquid

£ 300 >300

50 50


300 150

1700 400

175 175

30 30

5 5






Gas

£ 300 >300

5 5


200 100

35 (100)2) 35 (5)3)

100 100






* MW = megawatt thermal output
1) for fluidized-bed combustion
2) coke oven gas
3) liquid petroleum gas

2 and NOx Emissions"Appendix A-6 - SO2 and NOx Emissions

Conversion Chart



To: (Multiply by) (r)



















To convert






















From ¯


mg/


ppm

ppm

g/GJ

g/GJ

g/GJ

lb/106 Btu



lb/106 Btu

lb/106 Btu











NOx

SO2

CoalA

ilOilB

GasC

CoalA



OilB

GasC









mg/m³



1

0.487

0.350

0.350

0.280

0.270

8.14 x 10-4



6.51 x 10-4

6.28 x 10-4









ppm Nox



2.05

1

0.718

0.575

0.554

1.67 x 10-3



1.34 x 10-3

1.29 x 10-3









ppm SO2



2.86

1

1.00

0.801

0.771

2.33 x 10-3



1.86 x 10-3

1.79 x 10-3









CoalA

2.86


1.39

1.00

1

2.33 x 10-3











g/GJ

OilB

3.57


1.74

1.25

1



2.33 x 10-3









GasC

3.70


1.80

1.30

1



2.33 x 10-3









CoalA

1230


598

430

430

1











lb/106 Btu

OilB

1540


748

538

430



1









GasC

1590


775

557

430



1









A:- Coal:- Flue Gas dry 6 % excess O2: Assumes 350 Nm³/GJ - ref IEA Paper 1986.
B:- Oil:- Flue Gas dry 3 % excess O2: Assumes 280 Nm³/GJ - ref IEA Paper 1986.
C:- Gas:- Flue Gas dry 3 % excess O2: Assumes 270 Nm³/GJ - ref IEA Paper 1986.

Appendix A-6 - Emission limits for new, large-scale, coal-fired power plants in various countries, plus pertinent EC and World Bank standards

Appendix A-6 Emission limits for new, large-scale, coal-fired power plants in various countries, plus pertinent EC and World Bank Standards

Country

SO2 emissions [mg/m³]

Size of plant

NOx emissions [mg/m³]

Size of plant

CO emissions [mg/m³]

Size of plant

Dust emissions [mg/m³]

Size of plant

EC

400

> 500 MWt

650

> 50 MWt

50

> 500 MWt

World Bank

500 t/d or 50 µg/m³ additional immission over slight prior SO2 burden (£ 50 µg/m³) 100 t/d or 10 µg/m³ additional immission over high prior SO2 burden (> 100 µg/m³)


858 (780 for lignite)

100 (150 in rural areas and when immission < 260 µg/m³ beyond power plant perimeter)


Australia

200

800

> 30 MWt

1000

80

-

Austria

80 % (sep. efficiency)

> 200 MWt

800

> 50 MWt

250

> 2 MWt

50

> 50 MWt

Belgium

400

> 300 MWt

200

> 100 MWt

50

> 50 MWt

Canada

740

740

125

Denmark

860

> 50 MWt

1150

> 50 MWt

57

> 5 MWt

Finland

140

> 150 MWt

200

> 300 MWt

57

> 50 MWt

France

1700 - 3400

(regional)

130

> 9.3 MWt

Germany

400

> 300 MWt

200

> 300 MWt

250

> 50 MWt

50

> 5 MWt

Great Britain

90 % (sep. efficiency)

> 700 MWt

760

> 700 MWt

97

> 700 MWt

India

height of stack > 500 MWt: 275 m > 200 < 500 MWt: 200 m < 200 MWt: (equation)


no limits


150 (350 for plants with < 200 MWt in unprotected areas)


Italy

400

> 100 MWt

650

> 100 MWt

50

> 100 MWt

Japan

plant-specific


411

> 70000 m³/h

50

> 200000 m³/h

New Zealand

125 - 500

> 5 MWt

Netherlands

400

> 300 MWt

400

> 300 MWt

50

Spain

2400

200

> 200 MWt

Sweden

290

430

35

USA

740

> 29 MWt

740

> 29 MWt

37

> 73 MWt

/.../ The minimum size of plant to which the relevant limit applies is stated in MWt; the volumetric flue-gas flow is stated in m³STP/h









Appendix A-7 - Minimum requirements as per German Federal water act (WHG*), section 7a

Appendix 47: Scrubbing of flue gases from combustion plant, Sept. 8, 1989

COD

Filterable substances4)

Fluoride

Sulfate

Sulfite

Lead

Cadmium

Chromium

Copper

Nickel

Mercury

Zinc

Sulfide

Accepted engineering practice





State of the art









General

805)

30

30

20000

20

0.1

0.05

0.5

0.5

0.5

0.05

1

0.2

1506)

mg/l

mg/l

mg/l

mg/l

mg/l

mg/l

mg/l

mg/l

mg/l

mg/l

mg/l

mg/l

mg/l

Hard-coal

1

power plants (pollutant concentr., mg/kg chloride)

see above

3.8 mg/kg

1.8 mg/kg

18 mg/kg

8 mg/kg

18 mg/kg

1.8 mg/kg

36 mg/kg

7.2 mg/kg

Lignite power plants with chloride contents up to 0.05 weight % (pollutant concentr., g/h)7)

see above

0.2 g/h

0.1 g/h

1 g/h

1 g/h

1 g/h

0.1 g/h

2 g/h

0.4 g/h

* WHG = Wasserhaushaltsgesetz
4) via quicklime
5) via limestone
6) pollutant concentration in g/h per 300 MW installed electrical output
7) after subtraction of the prior COD pollutant concentration introduced with the service water