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The '''peripheral nervous system''' or '''PNS''', is part of the [[nervous system]], and consists of the [[nerve]]s and [[neuron]]s that reside or extend outside the [[central nervous system]]--to serve the limbs and organs, for example. Unlike the [[central nervous system]] however, the PNS is not protected by bone or the [[blood-brain barrier]], leaving it exposed to toxins and mechanical injuries. The peripheral nervous system is divided into the [[somatic nervous system]] and the [[autonomic nervous system]].
A '''fossil fuel power plant (FFPP)''' (also known as steam electric power plant in the [[United States|US]], thermal power plant in [[Asia]], or power station in the [[United Kingdom|UK]]) is an energy conversion center designed on a large scale for continuous operation. Just as a [[battery (electricity)|battery]] converts relatively small amounts of [[chemical energy]] into [[electricity]] for temporary or intermittent use, the FFPP converts the sun's energy stored in [[fossil fuels]] such as [[coal]], oil, or [[natural gas]] successively into thermal energy, mechanical energy, and finally electric energy for continuous use and distribution across a wide geographic area. Each FFPP is a highly complex, custom designed system. Present construction costs ([[2004]]) run to $1300/kW, or $650 million USD for a 500 [[MWe]] unit. Multiple generating units may be built at a single site for more efficient use of land, resources, and labor. The operational descriptions below are typical for a large plant and will vary from one plant to the next.
== Naming of specific nerves ==
==Fuel transport and delivery==
Coal may be delivered by transport [[truck]] or [[railroad]] cars. A large coal [[train]] may be nearly a mile long, containing 100 cars, each with 100 tons of coal, for a total load of 10,000 tons. Modern unloaders use rotary dump devices. The unloader includes a train positioner arm that moves the entire train to position a car over a coal hopper. The dumper clamps an individual car against a platform, which swivels the car upside down to dump the coal. Swiveling couplers enable the entire operation to occur while the cars are still coupled together. Unloading a train takes about three hours. Older unloaders may still use bottom dump rail cars. Generating stations adjacent to a mine sometimes haul coal with massive [[diesel-electric]] drive trucks with 140 ton capacity. Trucks this large typically have 8 ft (2.5 m) diameter tires, too big and heavy to be licensed for highway use.
The 12 [[cranial nerves]] originate from the [[brainstem]], and mainly control the functions of the anatomic structures of the head with some exceptions. CN X receives visceral sensory information from the thorax and abdomen, and CN XI is responsible for innervating the [[sternocleidomastoid muscle|sternocleidomastoid]] and [[trapezius muscle]]s, neither of which are exclusively in the head.
For startup or auxiliary purposes, the plant may use no. 2 or no. 5 [[fuel oil]] as well, Fuel oil may be delivered by tanker truck or train car. It is stored in vertical cylindrical steel tanks as large as 90,000 barrels (14,000 m<sup>3</sup>). The [[viscosity|heavier]] no. 5 "bunker" fuel must be steam heated before pumping in cold climates.
[[Spinal nerve]]s take their origins from the [[spinal cord]]. They control the functions of the rest of the body. In humans, there are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. The naming convention for spinal nerves is to name it after the [[vertebra]] immediately above it. Thus the fourth thoracic nerve originates just below the fourth thoracic vertebra. This convention breaks down in the cervical spine. The first spinal nerve originates above the first cervical vertebra and is called C1. This continues down to the last cervical spinal nerve, C8. There are only 7 cervical vertabra and 8 cervical spinal nerves.
Natural-gas fuelled plants are usually built adjacent to gas transport pipelines or have dedicated gas pipelines extended to them.
==Cervical spinal nerves (C1-C4)==
==Fuel processing==
The first 4 cervical spinal nerves, C1 through C4, split and recombine to produce a variety of nerves that subserve the neck and back of head.
Coal is prepared for use by crushing the rough coal to pieces less than 2 inches (50 mm) size. The coal is transported from the storage yard to in-plant storage silos by rubberized [[conveyer belt]]s at rates up to 4000 tons per hour. A 400 ton silo may feed a coal pulverizer (coal mill) at a rate of up to 60 tons per hour. It is introduced into the top of the pulverizer which grinds the coal to a powder the consistency of face powder and blows powder mixed with air into the furnace. A 500 MWe plant will have six such pulverizers, five of which can supply coal to the furnace at 250 tons per hour under full load.
Spinal nerve C1 is called the [[suboccipital nerve]] which provides motor innervation to muscles at the base of the [[skull]].
C2 and C3 form many of the nerves of the neck, providing both sensory and motor control. These include the [[greater occipital nerve]] which provides sensation to the back of the [[head (anatomy)|head]], the [[lesser occipital nerve]] which provides sensation to the area behind the [[ear]]s, the [[greater auricular nerve]] and the [[lesser auricular nerve]]. See [[occipital neuralgia]].
The [[phrenic nerve]] arises from nerve roots C3, C4 and C5. It innervates the [[diaphragm (anatomy)|diaphragm]], enabling breathing. If the spinal cord is transected above C3, then spontaneous breathing is not possible. See [[myelopathy]]
== Brachial Plexus (C5-T1)==
==Feedwater heating==
The last 4 cervical spinal nerves, C5 through C8, and the first thoracic spinal nerve, T1,combine to form the [[brachial plexus]], a tangled array of nerves, splitting, combining and recombining, to form the nerves that subserve the arm and upper back. Although the brachial plexus may appear tangled, it is highly organized and predictable, with little variation between people. See [[brachial plexus injuries]].
The water used in the steam boiler is a means of transferring heat energy from the burning fuel to the mechanical energy of the spinning turbine. Because the metallic materials it contacts are subject to [[corrosion]] at high temperatures and pressures, the water is highly purified to remove impurities before use. A system of [[water softener]]s and [[ion exhange]] [[demineralizer]]s produces water so pure that it coincidentally becomes an electrical [[insulator]], with [[conductivity]] in the range of 0.3–1.0 microsiemens per centimeter. The purified water known as ''makeup water'' is added to the feedwater at perhaps 20 US gallons per minute (1 L/s) to make up for the small losses due to steam leaks in the system.
===Before forming three cords===
The feedwater cycle begins with condensate water being pumped out of the [[condenser]] after travelling through the [[steam turbine]]s. The flow rate at full load in a 500 MWe plant is about 6000 US gallons per minute (0.4 m<sup>3</sup>/s). The water flows through a series of six or seven intermediate [[feedwater heater]]s, heated up at each point with steam extracted from an appropriate duct on the turbines and gaining temperature at each stage. Typically the fourth heater is a [[deaerator]], which removes dissolved air from the water, further purifying and reducing its corrosivity. The water may be treated following this point with [[hydrazine]], a chemical which removes the last remaining [[oxygen]] in the water to below 5 parts per billion (ppb). It is also treated with [[pH]] control agents such as [[ammonia]] or [[morpholine]] to keep the residual [[acid|acidity]] low and thus non-corrosive.
The first nerve off the brachial plexus is the [[dorsal scapular nerve]], arising from C5 nerve root, and innervating the [[rhomboid]]s and the [[levator scapulae]] muscles.
The [[long thoracic nerve]] arises from C5, C6 and C7 to innervate the [[serratus anterior]].
The brachial plexus first forms three trunks, the superior trunk, composed of the C5 and C6 nerve roots, the middle trunk, made of the C7 nerve root, and the inferior trunk, made of the C8 and T1 nerve roots. The [[suprascapular nerve]] is an early branch of the superior trunk. It innervates the suprascapular and infrascapular muscles, part of the [[rotator cuff]]. See rotator cuff for [[rotator cuff|rotator cuff injuries]]
The trunks reshuffle as they traverse towards the [[arm]] into cords. There are three of them. The lateral cord is made up of fibers from the anterior and middle trunk. The posterior cord is made up of fibers from all three trunks. The medial cord is composed of fibers solely from the medial trunk.
==Boiler=[[Lateral operationcord]]===
The lateral cord gives rise to the following nerves:
The boiler is a rectangular [[furnace]] about 50 ft (15 m) on a side and 130 ft (40 m) tall. Its walls are made of a web of high pressure steel tubes about 2.3 inches (60 mm) in diameter.
*The [[lateral pectoral nerve]], C5, C6 and C7 to the [[pectoralis major]] muscle
*The [[musculocutaneous nerve]] which innervates the [[biceps brachii|biceps]] muscle
*The [[median nerve]], partly. The other part comes from the medial cord. See below for details.
===[[Posterior cord]]===
Coal is blown into the furnace from fuel nozzles at the four corners and it rapidly combusts, forming a large fireball at the center. This heats the water that circulates through the boiler tubes. The circulation rate in the boiler is three to four times the throughput, typically driven by four massive sealed pumps. As the water in the [[boiler]] circulates it absorbs heat and changes to steam at 700 °F (370 °C) and 3200 [[pound-force per square inch|lbf/in²]] (22.1 M[[Pascal|Pa]]), which is separated from the water by parallel plates inside a drum at the top of the furnace. The saturated (wet) steam is introduced into [[superheat]] pendant tubes hanging in the hottest part of the combustion gasses as they exit the furnace. Here the steam is superheated to 1000 °F (540 °C) to dry it and prepare it for the turbine.
The posterior cord gives rise to the following nerves:
*The [[upper subscapular nerve]], C7 and C8, to the [[subscapularis]] muscle of the [[rotator cuff]].
*The [[lower subscapular nerve]], C5 and C6, to the [[teres major]] also of the rotator cuff.
*The [[thoracodorsal nerve]], C6, C7 and C8, to the [[latissimus dorsi]] muscle.
*The [[axillary nerve]], which supplies sensation to the shoulder and motor to the [[deltoid]] muscle and the [[teres minor]] muscle.
*The [[radial nerve]], which innervates the [[triceps brachii]] muscle, the [[brachioradialis]] muscle, the extensor muscles of the fingers and wrist ([[extensor carpi radialis]] muscle), and the extensor and abductor muscles of the thumb. See [[radial nerve injuries]].
===[[Medial cord]]===
Plants designed for [[lignite]] or brown coal are increasingly used in locations as varied as [[Germany]], [[Victoria, Australia]], and the midwestern US. Lignite is a much younger form of coal than black coal. It is less dense than black coal and requires a much larger furnace for equivalent heat output. Such coals can be up to 70% water and ash, yielding lower furnace temperatures and requiring larger induced draft fans. The firing systems also differ from black coal, and typically draw hot gas from furnace exit level and mix it with the coal in fan-type mills that exhaust the pulverised coal/hot gas mix into the boiler.
The medial cord gives rise to the following nerves:
*The [[median pectoral nerve]], C8 and T1, to the pectoralis muscle
*The [[medial brachial cutaneous nerve]], T1
*The [[medial antebrachial cutaneous nerve]], C8 and T1
*The [[median nerve]], partly. The other part comes from the lateral cord. C7, C8 and T1 nerve roots. The first branch of the median nerve is to the [[pronator teres]] muscle, then the [[flexor carpi radialis]], the [[palmaris longus]] and the [[flexor digitorum superficialis]]. The median nerve provides sensation to the anterior palm, the anterior [[thumb]], [[index finger]] and [[middle finger]]. It is the nerve compressed in [[carpal tunnel syndrome]].
*The [[ulnar nerve]] originates in nerve roots C7, C8 and T1. It provides sensation to the ring and pinky fingers. It innervates the [[flexor carpi ulnaris]] muscle, the [[flexor digitorum profundus]] muscle to the ring and pinky fingers, and the intrinsic muscles of the hand (the [[interosseous muscle]], the [[lumbrical muscle]]s and the [[flexor pollicus brevis]] muscle). This nerve traverses a groove on the elbow called the [[cubital tunnel]], also known as the funny bone. Striking the nerve at this point produces an unpleasant sensation in the ring and little fingers.
==Other thoracic spinal nerves (T3-T12)==
==Steam turbine generator==
The remainder of the thoracic spinal nerves, T3 through T12, do little recombining. They form the [[intercostal nerve]]s, so named because the run between the [[rib]]s. For points of reference, the 7th intercostal nerve terminates at the lower end of the [[sternum]], also known as the [[xyphoid process]]. The 10th intercostal nerve terminates at the [[umbilicus]], aka the belly button.
The turbine generator consists of a series of steam turbines interconnected to each other and a generator on a common shaft. There is a high pressure (hp) turbine at one end, followed by an intermediate pressure (ip) turbine, two low pressure (lp) turbines, and the generator. As steam moves through the system and drops in pressure, it expands in volume, requiring larger diameter and longer blades in each succeeding turbine to extract the remaining energy. The entire rotating mass may be over 200 tons and 100 ft (30 m) long. It is so heavy that it must be kept turning slowly even when shut down (3 rpm) so that the shaft will not sag even slightly and become unbalanced. This is so important that it is one of just four functions of blackout emergency power batteries on site: [[emergency lighting]], [[communication]], station alarms, and turbine generator turning gear.
== Pelvis and Perineum Nerves ==
In operation, the superheated steam from the boiler passes through 14–16 in (350–400 mm) diameter piping down to the hp turbine, where it falls in pressure to 600 lbf/in³ (4 MPa) and 600 °F (315 °C), exits through 24–26 in (600–650 mm) diameter cold reheat lines and passes back up into the boiler where the steam is reheated in special [[reheat pendant tubes]] back to 1000 °F (540 °C). The hot reheat steam is conducted down to the ip turbine where it falls again in both [[temperature]] and [[pressure]], and exits directly to the large bladed lp turbines, and finally enters the [[condenser]].
*Lumbar spinal nerves
The generator, 30 ft (9 m) long and 12 ft (3.7 m) diameter contains a stationary [[stator]] and a spinning [[rotor]], each containing miles of heavy [[copper]] conductor— no permanent [[magnet]]s here. In operation it generates up to 21,000 [[ampere|amps]] at 24,000 [[volts]] [[Alternating current|AC]] (504 MWe), as it spins at 3600 rpm, synchronized to the 60 Hz [[power grid]]. (The power grid frequency is 60 Hz across the United States and Canada, typically 50 Hz in Europe and parts of Japan.) This electricity flows to a distribution yard, where [[transformer]]s step the voltage up to 115, 230, 500, or 765 kV AC as needed for transmission to its destination. The rotor spins in a sealed chamber cooled with [[hydrogen]] gas, selected because it has the highest known [[heat transfer coefficient]] of any gas. This system requires special handling during startup, with air in the chamber displaced by [[carbon dioxide]] first, before filling with hydrogen. This ensures that the highly [[flammable]] hydrogen will not mix with [[oxygen]] in the air.
*Sacral spinal nerves
*Coccygeal spinal nerves
==Steam condensingSee also ==
* [[Peripheral nervous system disease]]
The exhausted steam exiting the low pressure turbines contacts condenser tube bundles which have cooling water circulating through them. This condenses the steam back to water, so rapidly that it creates a partial vacuum of 1.5–2.0 in Hg (5–7 kPa) in the condenser. The vacuum in effect creates a force which sucks the steam from the last stages of the turbines. From the bottom of the condenser, powerful pumps force the condensate back to the feedwater heaters to restart the cycle. The waste heat in the separate cooling water circuit must be removed to maintain its ability to cool as it circulates. This is done by pumping it through either natural draft or forced draft [[cooling tower]]s, which reduce the temperature 20–30 °F (11–17 °C) by evaporation. The circulation flow rate of the cooling water in a 500 [[MWe]] unit is about 120,000 US gallons per minute (7.6 m<sup>3</sup>/s) at full load.
==Stack gas path & cleanup==
As the combustion gas exits the boiler it is routed through a rotating flat basket of metal mesh which picks up heat and returns it to incoming fresh air as the basket rotates, This is called the [[air preheater]].
The gas exiting the boiler is laden with [[fly ash]], which are tiny spherical ash particles, and contains the [[carbon dioxide]], [[sulfur dioxide]], and [[nitrogen oxide]] combustion gasses. The fly ash is removed by [[fabric bag filters]] or [[electrostatic precipitator]]s. Once removed, the fly ash byproduct can sometimes be used in manufacture of [[concrete]]. Where required by law, the sulfur and nitrogen oxide [[pollutant]]s are removed by [[stack gas scrubber]]s which use a pulverized [[limestone]] or other [[alkaline]] wet slurry to neutralize and wash the acid gases out of the exit stream. The gas travelling up the [[smoke stack]] may by this time only have a temperature of about 120 °F (50 °C). The smoke stack may be 500–600 ft (150–180 m) tall to dilute and disperse the remaining smoke components in the atmosphere.
{{nervous_system}}
==Super critical steam plants==
Above the [[critical point]] for water of 705 °F (374 °C) and 3212 lbf/in³ (22.1 MPa), there is no [[phase transition]] from water to steam, but only a gradual decrease in [[density]]. [[Boiling]] does not occur and it is not possible to remove impurities via steam separation. In this case a new type of design is required for plants wishing to take advantage of increased [[thermodynamic efficiency]] available at the higher temperatures. These plants (also called ''once-through'' plants because boiler water does not circulate multiple times) require additional water purification steps to ensure that any impurities picked up during the cycle will be removed. This takes the form of high pressure ion exchange units called [[condensate polisher]]s between the steam condenser and the feedwater heaters.
[[Category:Nervous system]]
[[Nuclear power plant]]s generally cannot reheat process steam due to safety requirements for isolation from the reactor core. This limits their thermodynamic efficiency to the order of 34–36%. Subcritical fossil fuel power plants can achieve 36–38% efficiency. [[Super critical]] designs have efficiencies in the low to mid 40% range, with new "ultra critical" designs using pressures of 30 MPa and dual stage reheat reaching about 48% efficiency.
[[Category:Peripheral nervous system|*]]
[[de:Peripheres Nervensystem]]
==Gas turbine combined cycle plants==
[[es:Sistema nervioso periférico]]
An important class of fossil power plant uses a [[gas turbine]], sometimes in conjunction with a steam boiler "bottoming" cycle. The efficiency of a combined cycle plant can approach 60% in large (500+ MWe) units. Such turbines are usually fuelled with [[natural gas]] or light fuel oil. While highly efficienct and very quick to construct (a 1000 MW plant may be completed in as little as two years from start of construction), the ecnomics of such plants is heavily influenced by the volatile cost of natural gas.
[[fr:Système nerveux périphérique]]
[[is:Úttaugakerfið]]
Simple-cycle gas turbine plants, without a steam cycle, are sometimes installed as emergency or peaking capacity; their thermal efficiency is much lower. The high running cost per hour is offset by the low capital cost and the intention to run such units only a few hundred hours per year.
[[lt:Periferinė nervų sistema]]
[[sv:Perifera nervsystemet]]
==External links==
*[http://www.processassociates.com/bookshelf/units/power_plant_1.htm Power Plant Reference Books]
[[Category: electric power]]
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