INTRODUCTION AND CLASSIFICATION OF FUELS

Transcription

1 Chapte 2 INTRODUCTION AND CLASSIFICATION OF FUELS 1. INTRODUCTION AND CLASSIFICATION OF FUELS A substance which poduces heat is called a fuel. The heat may be poduced eithe by combustion o by nuclea fission and fusion. Heat geneated by the combustion of fuel is utilized eithe diectly o is conveted into mechanical o electical enegy. Classification of fuels: It was accepted to classify the fuel. 1- With espect to its state. 2- With espect to the method of its poduction. With espect to the state fuels ae divided into thee goups: a) Solid fuel (Wood, coal, peat, coke, etc). b) Liquid fuel (Cdue oil, ta, Mazut,.etc). c) Gaseous fuels (natual gas, coke oven gas, blast funace gas, poduce gas). Fuels with espect to the method of poduction ae subdivided into two goups: 1-Natual fuel. 2-Manufactued fuel. Only two kinds of natual fuels ae used fo metallugical funaces: the natual gas and cude oil (afte teatment). As fo manufactued fuel the following kinds ae widly used: 1- Gaseous fuel (blast funaces gas, coke oven gas, mixed blast funace and coke oven gas, mixed natual and blast funace gas. 2- Liquid fuels (Mazut, ta). 3- Solid fuels (coke, coal dust) coke is mainly used in blast funace and cupola, coal dust is mainly used fo funaces of non feous metallugy. At pesent the solid fuels ae substituted by gaseous fuel. 46

2 2. ORIGIN, COMPOSITION, CHARACTERISTICS AND SIGNIFICANCE OF CONSTITUENTS OF COAL Oigin of Coal: Coal is a complex mixtue of plant substances alteed in vaying degee by physical and chemical pocesses. These pocesses which changed plant substances into coal has taken million of yeas and has been accomplished by bacteia, heat and pessue inside the eath s cust. Composition of Coals: Composition of coal is expessed in tems of its poximate and ultimate analysis. Poximate analysis of coal means detemining the pecentage of moistue, volatile matte, fixed cabon and ash. Poximate analysis with sulphu content and heating value of coal helps in deciding the mode of utilization of a paticula coal. A typical composition of diffeent types of coals and some othe fuels is given in the Table. 2. The change in aveage composition fom wood peat lignite coals anthactice (on dy ash fee basis) is given in table 2. Table 2: Composition change fom wood to Anthacite Wood Peat Lignite Fuels Sub-bituminous coal Bituminous coal Semi-bituminous Anthacite % Composition on dy ash fee (daf) basis Caloific valve (daf), Cabon Hydogen Nitogen Oxygen kcal/kg Moistu e at 60% R.H. and 40 o C,%

3 Moistue Fixed cabon Volatile mate As epoted Dy basis INTRODUCTION AND CLASSIFICATION OF FUELS Table 3 Typical composition of diffeent types of coal. Poximate analysis, % Ultimate Analysis, % Caloific valve kcal/kg Fuels Ash C H 2 O 2 N 2 S Ash Peat Lignite Bituminous coal: -Low volatile Medium volatile High volatile Sub bituminous Semianthacite Anthacite Pine wood Oak wood, dy Coke (by poduct oven) Coke beeze (0-15 mm) Chacoal COMPOSITION OF SOLID AND LIQUID FUELS Fo solid and liquid fuels both the technical composition on and the elementay chemical composition is detemined. Technical analysis of the solid fuels consists of the detemination of 1-moistue content (w) 2-ash content (A) volatile mattes content which ae the gaseous poducts of the fuel decomposition at high tempeatue and 4-Coke content (the solid emainde afte heating the fuel sample at t=850 o C without ai). Besides the content of sulphu (S) and caloific value of fuel is detemined while technical analysis of the solid fuels. Fo liquid fuels the viscosity tempeatue of solidification must be detemined additionally. 48

4 Due to the vey complicated chemical composition of the solid and liquid fuels and a lage numbe of the chemical combinations fom which they consist of the chemical composition of solid and liquid fuels is caied out with espect to the chemical elements (elementay chemical analysis). Elementay analysis consists of the detemination of the main elements cabon (C) hydogen (H) Oxygen (O) nitogen (N) sulphu (S) and the content of moistue (W) and ash (A). On the base of the elementay chemical analysis of solid and liquid fuels the following kind of fuel mass ae distinguished: 1- Oganic mass (O). 2-Combustible mass (C). 3-Dy fuel (D) and 4- as eceived moist fuel (2). The composition of each fuel mass is shown in table (1). Index C H O N S A W Z O Oganic mass C Combustible mass A Dy fuel Z O eceived moist fuel The composition of each mass in pecentage by weight may be expessed as follow: 1- Oganic mass C O + H O + O O + N O = % (1) 2-Combustible mass 3-Dy fuel C C + H C + D C + N C + S C = % (2) C d + H d + O d + N d + S d A d = % (3) 4-As eceived fuel: C + H + N + D + S + A + W = % (4) The content of any element given fo the one fuel mass may calculated fo the othe mass if the convesion facto fo these two masses known: 1-Oganic mass into combustible mass oc S c 49

5 2-Oganic mass into dy mass d ( S od 3-Oganic mass into as eceived fuel A d ) ( S A o 4-Combustible mass into oganic mass 5-Combustible mass into oganic mass c o S c W ) (8) (7) cd 6-Combustible mass into as eceived fuel A a (9 7-Dy mass into oganic mass c ( A W ) (10) d o d ( S A d ) (11) 8-Dy mass into combustable mass 9-Dy mass into as eceived fuel d c A d (12) 10-As eceived fuel into oganic mass d W (13) o ( S A 11-As eceived fuel into combustible mass c ( A W W ) ) (15) (14) 12-As eceived fuel into dy mass d W (16) 50

6 Taking into account the convesion facto any fuel mass can be conveted into the othes by multiplying each component of a given mass by its convesion facto fo example: X o = X c c-o = X c X c = x o o-c = X o etc. By the way c-o = c S S c 1 o c -d = 1 and so on. d Significance of the Constituents of Coal: Moistue: In geneal high moistue content in coal is undesiable because: - It educes the caloific value of the fuel. - It inceases the consumption of the coal fo the heating puposes. - It lengthens the time of heating. - We pay fo it when the coal is puchased and tanspoted. But thee ae cetain specific cases whee moistue is delibeately added o is desiable to some extent e.g. - Dust nuisance is checked while loading, unloading, tanspoting and chaging coal into the oven when it is wet. - Moistue undegoes endothemic decomposition which educes the tempeatue of the hot coal bed (eithe when buning it on gate o duing the manufactue of poduce gas) theeby eliminating its fusion and clinke fomation which othewise would have blocked the passage of ai. - Sometimes, wate is spayed on the coal dust chaged in the coke oven. This apat fom checking dust nuissance duing coal chaging helps in potecting the methane and othe hydocabons pesent in the coke oven gas fom cacking in pesence of hot coke and othe oven walls because, it undegoes endothemic decomposition to educe the tempeatue of the coke oven gas as well as that of the coke mass theeby eliminating its fusion (called gaphitization). Volatile matte: 51

7 Cetain gases like CO, CO 2, CH 4, H 2, N 2, O 2, hydocabons etc. ae pesent in the coal which comes out duing its heating. These ae called the volatile matte of the coal. The coal with highe volatile matte content: - Ignites easily i.e. it has lowe ignition tempeatue. - Buns with long smoky yellow flame. - Has lowe caloific value. - Will give moe quantity of coke oven gas when it is heated in absence of ai. - Will equie lage funace volume fo its combustion. - Has a highe tendency of catching fie (due to low tempeatue exothemic oxidation) when stoed in open space. Fixed Cabon: It is the pue cabon pesent in the coal. Highe the fixed cabon content of the coal, highe will be its caloific value. In anthacites, the volatile matte is vey small and the values of fixed cabon and total cabon ae almost equal. In othe coals, fixed cabon is less that total cabon. The cabon content is detemined by Libel s method by completely buning the coal in a cuent of pue oxygen and finding the amount of esultant cabon dioxide. The cabon content of coal incease with inceases in the ank. Among the micoconstituents of the same coal, the exinites and vitinite have almost simila cabon content while fausinite has highe values. Total Cabon: It means the fixed cabon plus the cabon pesent in the volatile mattes e.g. in CO, CO 2, CH 4, hydocabons etc. Total cabon is always moe than fixed cabon in any coal. High total cabon containing coal will have highe caloific value. Hydogen: It inceases the caloific value of the coal. It is associated with the volatile matte of the coal. Also, the pecentage of NH 3 in the coke oven gas is moe if the coal fom which it has come out contains moe H 2. This NH 3 is ecoveed as (NH 4 ) 2 SO 4 by eacting NH 3 with H 2 SO 4 ) which is a valuable fetilize. Pat of the hydogen of coal emains as such in the coke oven gas theeby inceasing its caloific value. Also, if hydogen is to be emoved fom this coke oven gas fo poduction of NH 3 its availability will be moe if the coal with high H 2 content has been used fo the pupose. The content of hydogen in coals fom the peat to the bituminous stage vaies between 4.5 and 6.5% and is not elated to the ank. Beyond the bituminous stage, 52

8 the hydogen content shaply deceases to a value of 1-2% in anthacites. Among the micoconstituents, the exinites ae chaacteized by high, and the fusinites by low, hydogen contents. Nitogen. The nitogen in coal is pesent up to 1-3% and comes fom the poteins matte pesent in vegetable matte. Pesence of inet nitogen deceases the caloific value of the coal. Howeve when coal is cabonized (i.e. heated in absence of ai), its and H 2 and H 2 combine theeby poducing NH 3 which is ecoveed as (NH 4 ) 2 SO 4, a valuable fetilize. The popotion of extactable nitogen deceases with matuity of coal. The nitogen content does not bea any elation to the ank of coal. In most coals it is between 1 and 2%. Lowe values down to 0.5 and uppe values up to 2.5 ae also found. The nitogen in coal is useful in cabonization industies which ecove a pat of it as valuable by poducts like ammonia, ammonium sulphate. Sulphu: Though its pesence (mainly as sulphides) inceases the caloific value of the coal, but it has seveal undesiable effects. The oxidation poduct of sulphu (e.g. SO 2, SO 3, etc.) especially in pesence of moistue cause coosion (damage due to chemical and electochemical action) of the equipment and cause atmospheic pollution. Sulphu is highly undesiable in metallugical coal used in ion and steel making as it badly affects the popeties of ion and steel. It causes hot shotness of steel, i.e. cacking of steel suface duing hot olling. Sulphu is commonly pesent in coal in thee foms, viz. Pyitic, oganic and sulphate but occuence of sulphides and elementay sulphu in coal have also been epoted. Only oganic sulfu should be included in the ultimate analysis. Oxygen: The less the oxygen content, the bette is the coal as it educes its caloific value. It deceases fom lignite to anthacite as the matuity of the coal inceases. As the oxygen content of the coal inceases, it moistue holding capacity inceases and the caking powe deceases. The oxygen content of coal has a close elation to the ank. The fome deceases with the inceases in the latte. Among the mico components of the same coal, vitinite has the highest oxygen, fusinite the lowest, and exinites has the intemediate value. Phosphous. It is undesiable in metallugical coal as it badly affects the popeties of the inceases in the latte. Phosphous occus in small quantities coal. Indians coking coals have nomally less than 0.15% phosphoous which offes no poblem fo common use in ion and steel poduction. Chloine. It is pesent mainly as chloides in the coal. It educes the fusion point of the ash of the coal. It is substantially emoved duing washing of the coal. 53

9 Ash. Ash is the combustion poduct of mineal mattes pesents in the coal. It compises mainly of silica (SiO 2 ) alumina (AL 2 O 3 ) and feic oxide with vaying amounts of othe oxides such as CaO, MgO, Na 2 O etc. high ash content in coal is undesiable in geneal. A coal with high ash content: - is hade and stonge. -Has lowe caloific value. - Poduces moe slag (impuities) in the blest funace when coke made out of it is used theein. Ash content of the coal is educed by its washing. 4. THE STORAGE OF COAL OXIDATION AND SPONTANEOUS COMBUSTION Feshly mined high volatile coal when stoed in bulk undegoes low tempeatue atmospheic oxidation due to the pesence of methane and othe volatile matte on the suface. This exothemic oxidation causes the ise in tempeatue of the coal and if the heat is not emoved, a stage comes when coal begins to bun. This is called spontaneous combustion which leads to outbeak of fie in the stoed coal. If the tempeatue ise due to oxidation does not exceed a citical value (say 50 o C fo lignite and 80 o C fo bituminous coals), spontaneous combustion does not take place but the quality of coal is affected depending on the degee of oxidation. Low tempeatue oxidation of coal causes: - Deceases in its caking powe and caloific value. - Decease in cabon and hydogen content. - Deceases in its size gading. - Inceases in its oxygen content. - Fie, if the tempeatue ise exceeds the citical value, i,e. 70 o C. - Decease in gas and ta yields on its cabonisation. Oxidation of high volatile matte containing coal (i.e. low ank coal) is moe compaed to that of low volatile coals (high ank). That means the chances of catching fie in anthacite is less compaed to bituminous coal. As the matuity of the coal inceases, its tendency to catch fie duing stoage deceases. It is woth noting that the ate of oxidation doubles fo a ise in tempeatue of 10 o C. Low tempeatue oxidation is acceleated by: - Tempeatue ise. - Access to diffused ai. - Pesence of small paticles. 54

10 - Pesence of small paticles. - Pesence of poous o fiable paticles. - Stoage in lage heaps with small suface to volume atio. On the othe hand, low tempeatue oxidation is etaded by: - Cooling eithe by ventilation o wate spay. - Reducing access to ai, i.e. by stoage in compessed piles o stoage unde wate. - Reducing the size of the stoage piles so that heat losses by conduction and convection to the atmosphee is high thus peventing tempeatue ise of the stoed coal. Size and the atmosphee is high thus peventing tempeatue ise of the stoed coal. Size and natue of stoage piles is detemined by the ank and type of coal. The lowe the ank of. 5. USED OF COAL Coal is uses fo: - Diectly buning and getting heat. - Geneating steam fo poducing electicity (nealy 1 1b of coal is bunt to geneate of 1 kwh of electicity). - Diving ailway locomotives. - Manufactuing coke and coal gas (e.g. coke oven gas, poduce gas, wate gas, etc.). - Manufactuing synthetic liquid fuels. - Gasification to poduces nitogeneous fetilise fom synthesis gas. Non fuel uses of bituminous and lowe ank coals: - Poduction of activated cabon used fo decoloation of glyceine and petoleum poducts. - Teatment with stong sulphuic acid foms a basic exchange agent used in wate teatment pocess. - Uses as pigments fo paints. - Powdeed coal is used in dynamite. - Used as filte fo vaious puposes due to its lightness, chemical inetness and low cost. - Cabonisation of bituminous coal poduces chemical such as ta, benzol, ammonia and host of othe chemicals. - Used fo making cabon bushes. 55

11 - Used fo buning in domestic oven. Uses of peat: It can be cabonised to poduce gas and coke. It is also biquetted and uses as a domestic fuel. Uses of lignite : - Fo manufactue of poduce gas. - Fo geneation of electical powe. - Fo gasification to poduce nitogenous fetilize. Uses of anthacite coal: - Fo ecabonising steel. It is use: - Fo making cabon electodes, bushes, battey pats, esistos, cabon efactoy, coosion esisting stuctual mateials. - As file and paint pigment. - Fo blending with cooking coal to check its swelling and impoving the coke quality. 6. SELECTION OF COAL FOR DIFFERENT USES Thee ae vaious factos which ae to be taken into account befoe it is decided to use the coal fo a paticula puposes: Coal fo metallugical puposes (i.e. making coke). Cooking coals must - be stong and had. - Have low ash, sulphu and phosphoous content. - Be consistent, i.e. of unifom quality. Coals fo poducing gas: Gas coal should have: - high volatile matte content so that gas yield is moe. - Less ash content (aound 8%). - Less sulphu content (1-1.2%). - Weak cooking popeties so that coal bed does not fuse duing gasification. - High ash fusion tempeatue so that clinke fomation can be avoided. Coal fo ailway locomotives: It should be: - Lage, well sceened and fom smalls. 56

12 - Low in ash content. - Weakly coking. - Fee fom clinkeing touble, i.e. its ash fusion tempeatue should be high. Coals fo domestic ovens: The pefeed coals fo domestic ovens ae the lage gaded sizes of the highe volatile fee buning anks. It should be low in ash. Ash fusibility is not that impotant because the gate of the domestic oven seldom each a tempeatue high enough to cause clinking difficulties. Coals fo steam ising: A coal used in boiles fo buning and geneating steam is called steam coal. Almost all othe types of coal which ae not suitable fo cabonization o gasification can be used fo steam aising.. Coal fo combustion pactices: The descibable qualities in a coal fo combustion pactices ae: - Caloific value should be high. - Ash content should be low. - Moistue should be low. - Unifom size is desiable, fine dust and lage lumps ae objectionable. - Successive deliveies of coal should be as fa as possible of the same quality. 7. PROPERTIES AND TESTING OF COAL Poximate analysis of coal: Detemination of moistue, volatile matte, ash and fixed cabon in coal compises its poximate analysis. Detemination of moistue content in coal: Loss in weight of coal caused by heating of weighed quantity of coal sample fo one hou at 105 o C is the moistue content in coal. A known amount of finely powdeed coal sample is kept in a silica cucible and heated in a muffle funace at o C fo one hou. Thee afte the cucible is taken out, cooled in a dessicato and weighted. The pocess of heating, cooling and weighting is epeated a numbe of times till the constant weight of coal (anhydous) is achieved. The pecentage of moistue is given by: loss in weight of coal % Moistue in coal x Weight of coal initially taken 57

13 Detemination of volatile matte in coal: It is the loss in weight of moistue fee powdeed coal when heated in a cucible fitted with cove in a muffle funace at 950 o C fo 7 minutes. loss in weight of moistue fee coal % Volatile matte x Weight of moistue fee coal Detemination of ash in coal: It is the weight of esidue obtained afte buning a weighed quantity of coal in an open cucible (i.e. in pesence of ai) at 750 o C in a muffle funace till a constant weight is achieved. Weight of esidue ash fomed % Ash in coal x Weight of coal initially taken Detemination of fixed cabon: It is detemined indiectly by deducting the sum total of moistue, volatile matte and ash pecentage fom. % fixed cabon in coal = (% moistue + % volatile matte + % ash). Ultimate analysis of coal: Detemination of total cabon, hydogen, nitogen, oxygen and sulphu pecentages in coal compises its ultimate analysis. Detemination of cabon and hydogen in coal: A known amount of coal is bunt in a cuent of dy oxygen theeby conveting C and H of coal into CO 2 (C + O 2 = CO 2 ) and H 2 O (H O 2 = H 2 O) espectively. The poducts of combustion (CO 2 and H 2 O) ae passed ove weighed tubes of anhydous calcium chloide and potassium hydoxide which absob H 2 O and CO 2 espectively. The inceases in the weight of CaCL 2 tube epesents the weight of wate (H 2 O) fomed while inceases in the weight of OH tube epesents the weight of CO 2 fomed. % of H and C in coal can be calculated as below: let, x = weight of coal sample taken. y= incease in the weight of CaCl 2 tube. z= incease in the weight of OH tube. Amount of cabon in the coal sample = sin ce, 44 of gms of cabon and 32 CO % cabon in coal 2 is gms of poduced oxygen C X 12 z fom 12 gms O 12X z 44 X x 2 32 CO X 2 44

14 Similaly, amount of hydogen in coal sample: Since, 18 gms of wate is fomed by 2 gms Of hydogen and 16 gms oxgen H 2 + hydogen in coal 2 X 18 X Detemination of nitogen in coal: Nitogen estimation in coal is done by kjeldahal s method. A known weight of powdeed coal is heated with concentated sulphuic acid in pesence of potassium sulphate and coppe sulphate in a long necked flask (called kjeledahal s flask) theeby conveting nitogen of coal to ammonium sulphate. When clea solution is obtained (i.e. when whole nitogen is conveted into ammonium sulphate) it is teated with 50% NaOH solution. The ammonia thus fomed is distilled ove and absobed in a known quantity of standad sulphuic acid solution. The volume of unused sulphuic acid is then detemined by titation against standad NaOH solution. Thus, the amount of acid neutalized by libeated ammonia (fom coal) is detemined: Since, (NH 4 ) 2 SO 4 + 2NaOH = NaSO 4 + 2NH 4 OH One litte of N/10 H 2 SO 4 consumed is equivalent to 0.1 gm mole of ammonia o 1.4 gm of nitogen. Volume of acid used = V 1 V 2 Whee V 1 = volume of H 2 SO 4 neutalized in blank, c.c. V 2 = volume of H 2 SO 4 neutalized in detemination, c.c Detemination of sulphu in coal. A known quantity of coal is bunt completely in bomb caloimete in a cuent of oxygen. Ash, thus obtained contains sulphu of the coal as sulphate which is extacted with dilute hydochloic acid and the acid extact is teated with baium chloide solution to pecipitate the sulphate as baium sulphate. X y x y 1 O2 2 H 2O 2 X volume of acid used x nomality % of nitogen in coal x Weight of coal taken 59

15 O2 BaCl 2 S SO4 BaSO 4 32gm 233 gms The pecipitate of BaSO 4 is filteed, washed, died and weighed fom which the sulphu in coal can be computed as follow: 32 gms sulphu in the coal will give 233 gms BaSO 4. If, x = weight of coal sample taken. and y = weight of BaSO4 pecipitate fomed. Then, amount of sulphu in coal sample: Detemination of oxygen in coal: It is deduced indiectly as follows. % oxygen in coal = (% of C + H + N + S + ash) Caloific value: so,% of sulphu It is defined as the quantity of heat libeated by the combustion of unit quantity of fuel. Pinciple of C.V detemination: When a weighed quantity of fuel is bunt in the caloimete, the heat libeated is used up in heating the caloimete and the wate in the caloimete. By equating the heat given out by the fuel with heat taken up by the caloimete and wate, the caloific value (also called heating value) is detemined. It is of two types viz. Highe (goss) caloific value and lowe (net) caloific value. Highe and lowe caloific values : in 32y y y coal X x Highe o goss caloific value. Hydogen is found to be pesent in almost all fuels and when the caloific value of such fuel is detemined hydogen is conveted into steam. Now, when the poducts of combustion ae condensed to oom tempeatue (25 o C), the latent heat of condensation of steam also gets included in the measued heat. The total value so calculated is known as highe o goss caloific value and thus may be defined as the total amount of heat libeated when one unit of the fuel is bunt completely and the combustion poducts ae cooled to oom tempeatue. Lowe o Net caloific value. In actual pactice, the wate vapos escape as such along with hot combustion gases and thus ae not condensed with the esult a 60

16 lesse amount of heat is available. The amount of heat, so available, is called as lowe o net caloific value and may be defined as the amount of heat libeated when one unit of the fuel is bunt completely and the combustion poducts ae allowed to escape. Thus, Units of caloific value: (i) fo solid and liquid fuels. Since solids and liquids ae measued in tems of thei masses, thei caloific values ae expessed as below. Caloies/ gm (in C.G.S. system).. Caloies/ kg (in M..S system). B.T.U./1b 1kcal/kg = 1.8 B.T.U / 1b (in F.P.S. o Bitish system). (ii) Fo gaseous fuels. Since gases ae measued in tems of thei volumes, thei caloific values ae expessed as below: kcal/ cubic mete (kcal/m 3 ) B.T.U. / cubic feet (B.T.U/FT 3 ) 1kcal / m 3 = B.T.U. / ft 3 1B.T.U/ ft3 = 9.3 kcal/m CARBONISATION OF COAL COE MAING AND BY PRODUCTS RECOVERY Cabonisation: Heating of coal in absence of ai to poduce coke is called its cabonization o destuctive distillation. ItS main pupose is to poduce coke wheeas the co-poduct is called coke oven gas fom which vaious liquid poducts like ta, benzol, naphthalene, phenol, anthacene etc. ae sepaated. Types of cabonization: Thee ae mainly two types of cabonization depending upon the tempeatue up to which the coal is heated in absence of ai namely. Low tempeatue cabonisation (LTC) and high tempeatue cabonisation (HTC). Thei salient featues ae tabulated below in Table. 4. low tempeatue cabonisation (LTC) Table 4. salient featue of LTC and HTC High tempeatue cabonisation (HTC) (a) It is caied out at 700 o C. (a) It is caied out at 1 o C. (b) It poduces semi coke which is used as a smokeless domestic fuel. It can sometimes be used in boile also to avoid smoke. (c) Yiled of coke oven gas is less in LTC. It is about Nm 3 gas/ ton dy coal. Less gas yiled is due to less devolatalisation of coal and less cacking of hydocabons at (b) It poduces metallugical coke fo use in blast funace and cupolas in foundy etc. (c) Yiled of coke oven gas is moe in HTC due to moe cacking of hydocabons (mainly methane in coke oven gas) at highe tempeatue. Yield is about Nm 3 /ton of dy coal. 61

17 lowe tempeatue of cabonisation. (d) Yiled of ta is high in low temp. cabonisation. It is about 10% of dy coal. (d) Ta yiled is less hee. It is about 3% of dy coal chaged. (e) Ammonia yield is low. (e) Ammonia yiled is moe (10-15 gm/nm 3 of coke oven gas) (f) Caloific value of coke oven gas poduced in LTC is moe due to highe pecentage of methane and unsatuated hydocabons in it. C.V. is about kcal/nm 3. (g) The ta poduced is aliphatic in natue. It contains less quantity of aomatic ing compounds like benzen, toluence, naphthalene, phenol, anthacene etc. howeve, ta acid content is highe. (h) Afte cabonisation, dischaging of coke is difficult as it swells a lot but does not shink much finally at the end of coking due to lowe tempeatue of cabonisation. (i) Fee cabon in ta (which esults fom the cacking of hydocabons) is less. It is about 5-10% of ta. Since cacking (HC H + C) is less sevee at lowe tempeatue. (k) Volatile matte content in coke is moe (5-7%) hence it is easie to ignite it because of lowe ignition tempeatue of high volatile matte containing coke. Ignition tempeatue of LTC coke is about 425 o C. (l) Hydogen content in coke oven gas is less (35-40%). Hence, diffeence in goss and net caloific value is less. (m) Coke yiled is moe. It is about 80% of dy coal. (f) C.V. of coke oven gas poduced in H.T.C is less. It is about kcal/ Nm 3 only due to lesse pecentage of hydocabons esulting fom its cacking at highe tempeatue of cabonisation. (g) Ta poduced has moe of aomatic ing compounds. (due to cystallisation eaction of staight chain compounds being favoued at highe tempeatue). (h) Dischaging of coke is easie as it shinks finally to a moe extent compaatively due to highe tempeatue of cabonisation. (i)coke poduced is stonge smalle in size and less eactive (due to low poosity) due to highe amount of shinkage of coke at highe tempeatue. (k) V.M. in coke is less (1-1-2%), hence its ignition tempeatue is moe. Ignition tempeatue of high temp. coke is about 605 o C. (l) H 2 content in coke oven gas is moe (55-60%). It is beneficial fo an adjoining nitogenous fetilise plant attached to steel plant which gets hydogen (fo ammonia making) fom coke oven gas by its cyogenic cooling. (m) Coke yield is less (about 77% of dy coal) 62