Module 2: Solid Fossil Fuel (Coal) Lecture 13: Coal liquefaction

Transcription

1 1 P age Mdule 2: Slid Fssil Fuel (Cal) Lecture 13: Cal liquefactin IIT Kharagpur NPTEL Phase II Web Curses

2 2 P age Keywrds: Direct cal liquefactin, indirect cal liquefactin, EDS prcess, H-cal prcess 2.5 Cal liquefactin Cal liquefactin is a prcess where cal is cnverted int liquid fuels, mainly t prvide substitutes fr petrleum prducts, which may be either used directly as fuel r cnverted int chemicals r ther liquid fuels. Cal liquefactin prcesses were first develped in the early 20th century. The crude petrleum rich cuntries may nt need this prcess fr fulfilling their requirement f liquid fuel but the cuntries which are lacking f crude but have a gd reserve f slid fuel like cal, a large scale applicatins f cal liquefactin prcess is entertained. The few cuntries, where this prcess is mainly running are Germany (during Wrld War II) and Suth Africa since the year 1960s. USA is als running cal t liquid fuel plant successfully. A plant using mre than six millin tns f cal annually culd prduce mre than 3.6 millin barrels f diesel and napththa. China has expended fifteen billin dllar fr cal t diesel fuel cnversin plant with the aim f replacing 10% f its il imprt with cal cnverted liquid ils by the year The threat f depletin f cnventinal il surces is anther majr reasn fr renewed interest in the prductin f il substitutes frm cal since last three decades. Hydrcarbn type liquid fuels are btained frm slid fuel like cal by the fllwing rutes mainly: 1) Hydrgenatin f cal 2) Slvent extractin f cal and hydrgenatin f cal extracts 3) Refining f tar and il btained frm carbnizatin f varius sild fuels and il shales 4) Gasificatin f slid fuels int synthesis gas and cnversin f the gas int liquid fuels and chemicals. IIT Kharagpur NPTEL Phase II Web Curses

3 3 P age The fllwing blck diagram (Figure 1) shws the ptins fr cal t liquid cnversin plants. Fig. 1. Different rutes f cal liquefactin Cal liquefactin can be achieved either by direct r indirect prcesses. The difference between these tw prcesses lies in that, the indirect liquefactin prcess needs t g thrugh gasificatin first, while, direct liquefactin prcess invlves prducing partially refined synthetic il frm cal. It is said by the technlgists that, indirect liquefactin is mre efficient than direct cal liquefactin techniques which are currently available Direct liquefactin Direct cal liquefactin was develped by Friedrich Bergius and it was started cmmercially in Germany near Wrld War II, t meet the huge demand f liquid fuel at that time. Bergius prcess was mdified and extended t fulfill tday s demand f liquid fuel. The cal is grund s that it can be mixed int cal derived heavy il recycled frm the prcess t frm a cal-il slurry feed. The slurry cntaining 30-50% cal is then heated in a reactr t abut 450 C IIT Kharagpur NPTEL Phase II Web Curses

4 4 P age in a hydrgen atmsphere between MPa pressures fr abut ne hur. Different catalyst used are tungsten r mlybdenum sulfides, tin r nickel leate. The reactin prduces heavy il, middle il, gasline and gases. One tnne f cal yields abut ne-half tnne f liquids. Prcesses have been develped t use cals frm lw rank lignites t high vlatile bituminus cals. Higher-rank cals are less reactive and anthracites are essentially nn-reactive. The liquids prduced have mlecular structures similar t thse fund in armatic cmpunds and need further upgrading t prduce specificatin fuels such as gasline and fuel il. Direct cal liquefactin is suitable fr a wide range f feeds: high vlatile bituminus cals sub-bituminus cals with lw ash lignites with lw ash Direct liquefactin is f tw types, single stage and tw stage prcesses. In single-stage direct liquefactin prcess, ne primary reactr is used t get distillates. Here a hydrtreating reactr is als jined alng with the primary reactr t imprve the quality f the distillate. The technlgy develpers are H-Cal (HRI, USA) Exxn dnr slvent (Exxn, USA) SRC-1 and II (Gulf Oil, USA) Cnc zinc chlride (Cnc, USA) IIT Kharagpur NPTEL Phase II Web Curses

5 5 P age Khleel (Ruhrkhle, Germany) NEDOL (NEDO, Japan) Tw reactrs in series are used in tw-stage direct liquefactin prcess. In the first stage, cal disslutin is dne where the prcess is perated either withut a catalyst r with a lw-activity dispsable catalyst. The heavy cal liquids prduced in the first reactr are hydrtreated in the secnd stage in the presence f a high-activity catalyst t prduce desired distillate. The prcess and technlgy develpers include Catalytic tw-stage liquefactin (US DOE and HTI, USA) Liquid slvent extractin (British Cal Crpratin, UK) Brwn cal liquefactin (NEDO, Japan) Cnsl synthetic fuel (Cnsl, USA) Lummus (Lummus, USA) Amng the different cmmercial prcesses, Exxn dnr slvent prcess (EDS) and H-cal prcess are discussed here. EDS (Exxn Dnr Slvent) prcess In this prcess cal slurry is prepared using a recycled slvent and the slurry is mixed with H 2, preheated and fed t a simple up-flw tubular reactr. The reactr perates at ºC and 2575 psig pressure. It is a nn-catalytic prcess. The ligher prduct naphtha, a middle distillate and a heavy distillate prduct are btained. Heavy distillate mixed with sme middle distillate frms the recycle slvent. The recycle slvent is hydrgenated in a fixed-bed catalytic reactr perated at C and 1600 psig H 2 pressure depending n the extent f hydrgenatin, where IIT Kharagpur NPTEL Phase II Web Curses

6 6 P age either nickel-mlybdenum r cbalt-mlybdenum n alumina supprt is used as a catalyst. A flw diagram f EDS prcess is described in Fig 2. Fig. 2. Flw diagram f EDS prcess H-cal prcess In this prcess, cal slurry is prepared with a recycle slvent that cnsists f a mixture f heavy and middle distillates btained by prduct fractinatin and slids cntaining hydrcracker prduct. H 2 is added t the slurry, the mixture is preheated and fed t an ebullated bed hydrcracker, which is the distinguishing feature f the prcess. The reactin cnditins are : temperature C and H 2 pressure 2900 psig. The catalyst used is either Ni-M r C-M IIT Kharagpur NPTEL Phase II Web Curses

7 7 P age supprted n alumina. The catalyst is fluidized by H 2 and a pumped internal recycle stream. This recycle stream cntains unreacted cal slids. Fig 3. Prcess flw diagram f H-Cal prcess H-cal prcess is described in Fig 3 in the frm f a flw diagram. The advantages f ebullatedbed reactr ver fixed-bed reactrs are that, the reactr cntents are well mixed and temperature can be mnitred and cntrlled in better way in the previus ne. IIT Kharagpur NPTEL Phase II Web Curses

8 8 P age References: 1. Fuels and cmbustin, S. Sarkar, 2 nd editin, Orient Lngman Ltd., Direct Cal Liquefactin Overview Presented t NETL, Jhn Winslw and Ed Schmetz, Lenard Technlgies Inc., US Department f Energy, March, IIT Kharagpur NPTEL Phase II Web Curses