Energy and the Environment Fall 2014 Instructor: Xiaodong Chu Email ： [email protected]...

Energy and the Environment

Fall 2014Instructor: Xiaodong Chu

Email ： [email protected] Tel.: 81696127, 13573122659

mailto:[email protected]

Fossil-Fueled Power Plants: Components

• Emission controlEmission control (排放控制 )– Nitrogen oxide controlNitrogen oxide control (氮氧化物控制 )

• The other major category of pollutants from fossil fuel combustion is nitrogen oxidesnitrogen oxides (氮氧化物 ), called NOx, which includes nitric oxide NOnitric oxide NO (一氧化氮 ), nitrogen dioxidenitrogen dioxide NONO22 (二氧化氮 ) (and its dimerdimer (二聚体 ) N2O4), nitrogennitrogen trioxidetrioxide NONO33 (三氧化氮 ) , pentoxidepentoxide NN22OO55 (五氧化二氮 ) , and nitrous oxide Nnitrous oxide N22OO (一氧化二氮 )

• NOx usually implies the sum of NO and NO2.

• NOx is a pernicious pollutant pernicious pollutant (有害污染物 ) because it is a respiratory tract irritant respiratory tract irritant (呼吸道刺激源 ) and it is a precursorprecursor (前驱体 ) toto photo-oxidants photo-oxidants (光氧化剂 ), including ozoneozone (臭氧 ) and acid deposition acid deposition (酸沉降 )

• Coal and oil contain organic nitrogen in their molecular structure and when burnt, these fuels produce fuel Nofuel Nox x (燃料型氮氧化物 )

• All fossil fuels produce thermal Nothermal Noxx (热力型氮氧化物 ), resulting from the recombination of atmospheric nitrogen and oxygen under conditions of the high temperatures prevailing in the flame of fossil fuel combustion

• There are basically two approaches to reducing sulfur emissions: during and after combustion of the fossil fuel



• During combustion, a low-NOx burner (LNB) employs a process called staged staged combustion combustion (分级燃烧 )

• NOx formation is a function of air-to-fuel ratio (by weight) in the flame



• Fuel (e.g., pulverized coal) and air is injected through the central annulusannulus ( 环 )of the burner and the air/fuel ratio is less than stoichiometric stoichiometric (化学计量比 ) , i.e., fuel-rich fuel-rich (富燃 ) , which produces a luminous flame luminous flame (发光火焰 ) , with some of the pulverized coal left unburnt, but also with low NOx formation

• Secondary and tertiary air arrives through outer annuliannuli ( 环 ), creating an outer flame envelope that is fuel-lean fuel-lean (贫燃 ) , where all the unburnt carbon burns up and less NOx is formed



• After combustion, in a selective catalytic reduction selective catalytic reduction (选择性催化还原 ) process either ammonia ammonia ( 氨 ) or urea urea (尿素 ) is injected into a catalytic reactorcatalytic reactor (催化反应器 ) through which the flue gas flue gas (烟气 ) flows

• In a selective noncatalytic reduction selective noncatalytic reduction (选择性非催化还原 ) , a reduction of NO can be accomplished at a higher temperature without a catalyst, where urea is used instead of ammonia

3 2 2 24NO+4NH +O 4N +6H O

2 2 2 2 2 24NO+4CO(NH ) (aq)+O 4N +4CO +2H O


• Emission controlEmission control (排放控制 )– Toxic emissions (毒性排放物 )

• Coal and oil contain mineral matter that during the combustion process may produce toxic vapors and particles

• Particles larger than 1–2 micronsmicrons (微米 ) in diameter are almost all captured by the particle removal system, either by an electrostatic precipitator or a fabric filter

• Smaller particles and vapors may escape through the smoke stack and pollute the environment

• Mercury Mercury ( 汞 ) , selenium selenium ( 硒 ) , cadmium cadmium ( 镉 ) , and arseniarsenic ( 砷 ) are semivolatilesemivolatile (半挥发性 ) toxic metals that escape through the smoke stack as vapors

• Another problem associate in part may do with coal-fired power plants is radonradon (氡 ) emissions, which is a disintegration product of uranium uranium ( 铀 ), the minerals of which may cling to the coal


• Waste disposalWaste disposal (废物处理 )– Coal-fired power plants produce a significant amount of solid waste – Oil-fired plants produce much less waste, and gas-fired plants produce

practically none– For some coals the fly ash fly ash (飞灰 ) and the scrubber sludge scrubber sludge (污泥 )

may contain toxic organic and inorganic compounds, for which the waste needs to be disposed of in a secure landfill and the landfill must be lined, with impenetrable materialimpenetrable material (不透材料 ) so that leachingleaching (浸出 )into the soil and groundwater is to be prevented


Pollutants emission


Pollutants and pollution control in coal fire power plant


Pollutants and pollution control in oil fire power plant


Pollutants and pollution control in gas fire power plant

Fossil-Fueled Power Plants: Advanced Cycles

• Combined cycle Combined cycle (联合循环 )


• Coal gasification combined cycle Coal gasification combined cycle (煤气化联合循环 )– A power plant using coal gasification and combined cycle is called an

integrated gasification combined cycle plant (IGCC)– Various coal gasification methods were developed already in the

nineteenth century for providing piped gas for home heating, cooking, and lighting

– Coal can be gasified to low-, medium- and high-heating value syngas– For an IGCC plant, high-heating value syngas is preferred


• Coal gasification combined cycle Coal gasification combined cycle (煤气化联合循环 )– The crushed coal is fed to a retort, where, in the presence of catalysts,

it is exposed to pure oxygen and steam

– To increase the heating value, the carbon monoxide and hydrogen is passed over a catalyst at about 400 ◦C to form principally methane methane (甲烷 ), a process called methanation methanation (甲烷化 )

– An alternative is the production of hydrogen in the water gas shift water gas shift reactionreaction (水煤气反应 )

2 2 23C+O +H O 3CO+H

2 4 23H +CO CH +H O

2 2 2CO+H O CO +H


• Cogeneration Cogeneration (热电联产 )– Cogeneration is applied to systems that provide both electrical power

and useful heat from the burning of fuel– In industrial or commercial installations the heat may be used for

space heating or material processing– The incentive for cogeneration is primarily financial in that the cost of

supplying electricity and heat via a cogeneration scheme might be less than supplying them separately

– Whether or not a cogeneration system reduces the amount of fuel needed to supply the electricity and heat depends upon the details of the cogeneration system


• Cogeneration Cogeneration (热电联产 )– When a heat engine drives an electric generator to produce

electricity, it also provides a stream of hot exhaust gas– Where the exhaust gas is warm enough to be used for process or

space heat, some of the exhaust gas enthalpy may be extracted to satisfy the heat requirement in a cogeneration plant

fuel el exQ P Q

el th fuelP Q

(1 )proc xch ex xch th fuelQ Q Q


• Fuel cellFuel cell(燃料电池 )– In a fuel cell, some of the chemical energy of the fuel is directly

converted into electrical energy, with the rest appearing as heat rejected to the environment

– Its theoretical thermal efficiency in terms of electrical energy generated versus fuel chemical energy input can be close to 100% when producing a low output of power

– Fuel cell hydrogen is usually generated by the reforming of methane reforming of methane (甲烷重整 )

Fossil-Fueled Power Plants

Energy and the Environment Fall 2014 Instructor: Xiaodong Chu Email ： [email protected]...

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