Bia agus Stíomáin Chuirtear isteach sa Chnámh
Tá comónta éagsúla ann i ciorcal uisce agus stíomha na boiler agus caithfimid eolas a bheith againn ar roinnt comónta ríthábhachtacha sa chiorcal seo. Is iad sin an Economizer, boiler drums, water tubes, agus an super heater.
Economizer
Economizer is a heat exchanger which takes heat from the flue gas, and increases the temperature of feed water coming from feed water common header to about the saturation temperature corresponding to the boiler pressure.
Throwing away the flue gases of high temperature into the atmosphere involves a great deal of energy losses. By utilizing these gases in heating feed water, higher efficiency and better economy can be achieved, and hence the heat exchanger is called “Economizer”.
Structurally economizer is a collection of bent hollow tubular elements through which feed water passes. Outside of the tubes are heated by Exhaust flue gases. More no. of water tubes more will be the heat exchange surface. No. of tubes and tube cross section are pre-designed as per required boiler parameters.
In the T-S curve above, the shadow portion illustrates the zone of economiser. The heat absorbed by feed water is denoted by ‘Qeco’.
Is comónta ríthábhachtach eile é an Ciorcal Uisce agus Stíomha
Boiler Drum.
Boiler Drums
Tá dhá shórt boiler drums ann a úsáidtear i gach sórt boiler, seodr stíomha agus seodr lúide. Tá gnách éagsúla ag an dá seodr.
Steam Drum
Is é seo na feidhmeanna atá ag an seodr stíomha i ciorcal uisce agus stíomha:
Chun uisce agus stíomha a stóráil go leor chun iarratais loada éagsúla a shiombailiú.
Chun ceannaireacht a thabhairt agus mar thoradh air, an ciorcal nádúrtha uisce a chur chun cinn trí water tubes.
Chun an stíomh a scuabadh ó mhéascán uisce-stíomha, a díoltaíonn na risers.
Chun cabhrú le trátálacha cheimiceacha chun O2 díoltas a bhaint amach agus pH riachtanach a choimeád.
Scuabadh an stíomh ó mhéascáin dhá phhas san seodr stíomha:
Caithfidh an stíomh a scuabadh ón méascán sula dtéann sé as an seodr, mar:
Léiríonn an uisce atá le haghaidh an stíomha soláithe dissolved. Sa super heater, fuair an uisce agus fágann an t-sóláit ar an taobh istigh den tuíp chun scáil a dhéanamh. Lúdaíonn an scáil an shaol ar an super-heaters.
D'fhéadfadh roinnt de na dúlra imchirt (mar shampla, silicíon vaporized) tabhairt faoi dhuilleoga turbine.
Is é ceann de na feidhmeanna tábhachtacha an seodr stíomha an stíomh a scuabadh ó mhéascán uisce-stíomha. Ag teasc íseal ( thíos 20 bar; 1 bar = 1.0197 kg/cm2) úsáidtear scuabadh gravta. Sa mhodh scuabadh gravta, díolaíonn na paiseáin uisce ón stíomh mar gheall ar an gcineáltaí.
Mar a théann an brú isteach sa seodr boiler, meastar an cineáltaí an stíomha, mar tá an stíomh an-dúshlánach. Mar sin, laghdóidh an difríocht idir an cineáltaí an stíomha agus an uisce. Mar sin, ní mór do scuabadh gravta a bheith neamheifeachta.
Mar sin, i seodr stíomha na boilears ard-bhrú, tá roinnt réiteach meicniúil (aitheanta mar seodr intreoir nó réiteach anti-priming) ann chun an stíomh a scuabadh ón uisce.
Léiríonn an pictiúr seo réiteach anti-priming éagsúla a úsáidtear i stáisiúnna forbartha téarmaí:
Is é an baffle an scuabadóir a scuabadh an méascán uisce-stíomha te ón stíomh scartha agus a thabhairt cosán treoraí don stíomh scartha.
Sa separator cyclone, cuireadh an méascán dhá phhas uisce-stíomha a imeacht ar bhealach héilíoch agus mar gheall ar fórsaí centrifugal, díolaíonn na paiseáin uisce ón méascán dhá phhas. Bhí na veainín beaga laistigh den separator cyclone ag bailiú na paiseáin uisce a díoltas.
Sa scrubber, cuireadh an méascán dhá phhas a imeacht ar bhealach zigzag agus sé a thabhairt an staid deiridh do scuabadh an stíomha.
Tar éis an scrubber, cuireadh an stíomh a imeacht trí screán perforated chuig an super-heater.
Mud Drum
Mud drum is another header which is situated at the bottom of the boiler and usually helps in natural circulation of water through the steam tubes. Mud drum usually contains water at saturation temperature, and also the precipitated salts and impurities known as slurries. It is periodically washed to remove the slurry by opening the discharge valve.
Water Tubes
These are also essential for feed water and steam circuit of boiler
Water tubes are bent or straight hollow tubes through which steam water mixture circulates. There are two types of water tubes, viz. down-comer and riser. This down comer, riser assembly is also known as Evaporator (or boiler proper). In the evaporator actual state change from water to steam occurs. In the T-S diagram beside, the zone of evaporator is illustrated. ‘Qeva’ is the heat absorbed by evaporator. It is mainly the latent heat of vaporization of water.
Down comers Water Tubes
As the name suggests down-comers are the water tubes through which water comes down from steam drum to mud drum (see fig.). No vapour bubble should flow along with saturated water from the drum to the down comers. This will reduce the density difference and the pressure head for natural circulation.
Risers Water Tubes
Risers are the water tubes through which steam water two-phase mixture at saturation temperature goes up from mud drum to steam drum. Risers are usually close to furnaces, while the down-comers are away from the furnaces.
Super Heaters
