FIELD OF INVENTION

[0001] The present disclosure, in general, relates to a
method of startup of coal gasification plant to generate methanol and more particularly, to independent and fast starting of methanol plant utilizing fluidized bed coal gasification, operating in air blown and/or Oxygen blown mode to generate syngas.
BACKGROUND AND PRIOR ARTS
[0002] Syngas (Synthetic gas), a fuel gas mixture is a
major source of production of methanol. Coal/ biomass gasification for the generation of syngas and subsequent production of methanol, is an excellent option when coal availability is abundant and other feed stocks such as natural gas or oil are not sufficiently available.
[0003] For the thermochemical production of syngas from
coal/ biomass, essentially three methods of gasification are known. They are- a. Fixed bed and moving bed gasifiers, which are used for low gas production especially for local power generation and coke oven gas generation; b. Entrained flow gasifier which is used in particular for generation of syngas and methanol production from low ash content coal (less than 25 wt%); c. Fluidized bed reactors/ gasifiers which are required for methanol production from syngas which is particularly generated from high ash content coal.
[0004] In the above three types of gasifier systems stated,
only oxidant (Oxygen), steam and coal are required for gasification in the first two types without the need for any inert medium such

as CO2 or steam. However, since high ash content coal is the feedstock that is readily available for use in India for the production of methanol, the first two types of gasifiers are unsuitable to be incorporated in the system of coal to methanol plant.
[0005] In case of generation of methanol from high ash
content coal by the fluidizing bed gasifier, it requires an inert fluidizing medium such as CO2 or steam for fluidizing the coal/ biomass. CO2 as a fluidizing medium is preferred over steam since CO2 is available as a product of the coal to methanol process whereas a separate steam generator is required when steam is used. The present invention relates to independent generation of CO2 required for starting of the fluidized bed gasifier in Oxygen blown mode by operating said gasifier in air blown mode, utilizing the syngas generated from the air blown mode for carrying out reduction of water gas shift reactor, CO2 capture and activation of methanol reactor to reduce the startup time of entire coal to methanol plant.
[0006] The existing art includes some methods of
startup of plants to produce syngas. Some of these prior art
methods include US4728506A which discloses a low energy
startup procedure for ammonia plant which produces hydrogen
containing synthesis gas from hydrocarbon feedstock, particularly
natural gas or light naptha. The said startup procedure for
ammonia plants employs ammonia as the startup media thereby
avoiding BTU loss associated with venting unconverted
hydrocarbons and the threat to catalyst beds associated with rapid buildup of temperatures therein. However, the method disclosed is not related to the startup and production of methanol from coal, is

optimized to work with natural gas or light naptha as the hydrocarbon feedstock and does not present any way of reducing time of startup of the ammonia plant.
[0007] Further, in another existing procedure
US6872867B1, the method discloses the startup of a plant which converts methanol into its derivatives specifically methanol to olefin. In the said method, a catalytic conversion process using a fluidized conversion zone, which requires a minimum superficial gas velocity to function properly, and a motor-driven, capacity-limited product compressor zone is started up using a thermal compressor by establishing two start-up gas recirculation circuits, one using the product compression zone running at high pressure to recirculate about 40 to 60 vol-% of the effluent gas stream from the conversion zone and the other running at low pressure and carrying the remaining portion of the effluent gas stream from the fluidized conversion zone where the high pressure circuit supplies motive gas to the thermal compression zone and the low pressure circuit supplies suction gas to the thermal compressor and the resulting compressed discharge gas enables the catalytic process to start up without the use of a dedicated motor-driven start-up compressor. However, the method disclosed does not relate to the production of methanol from coal or a unique way of utilizing the fluidizing zone for methanol production.
[0008] Another procedure included in US7855235B2
provides a method to start an integrated, low cost process to produce hydrocarbons, especially normally liquid hydrocarbons, from natural gas or associated gas, in particular at remote locations as well as at off-shore platforms. The said invention further provides a process for producing normally gaseous,

normally liquid and optionally normally solid hydrocarbons from synthesis gas in a process that involves using at least a portion of the gaseous hydrocarbons produced as a recycle stream to which hydrogen is added prior to its reintroduction into the reactors and as the activity of the catalyst converting the synthesis gas proceeds from start-up towards a steady state, the amount of recycle stream is reduced. However, this invention uses natural gas as a source material to produce syngas along with the addition of hydrogen to hydrocarbons which does not relate to our proposed method of methanol production from coal gasification by fluidized bed reactor.
[0009] Another existing procedure includes
US4473622A, where the method relates to a methanol-to-hydrogen cracking reactor for use with a fuel cell vehicular power plant. The said system is particularly designed for rapid start-up of the catalytic methanol cracking reactor after an extended shut-down period, i.e., after the vehicular fuel cell power plant has been inoperative overnight. This invention relates to the startup of the catalytic methanol cracking reactor and hence does not relate to our proposed method of utilization of fluidized bed gasification for coal to methanol production.
[0010] The procedure disclosed in US6123873A
describes a method for initiating operation of an auto thermal reformer including the steps of preparing a hot gas which is rich in hydrogen by contacting a methanol and steam containing feed gas with a methanation catalyst and introducing the hot gas into the auto thermal reformer, thereby heating the reformer with heat contained in the hot gas to a temperature which is sufficiently high to initiate and maintain subsequent reforming reactions to be

carried out in the reformer. However, this invention relates to the heating of the catalyst of the reformer and therefore does not relate to our proposed method.
[0011] Further, the method described in CN103626128
discloses a quick-start system for preparing hydrogen from
methanol and water. The system comprises a liquid storage
container, a raw material conveyer, a quick-start device, hydrogen
preparation equipment and a membrane separation device,
wherein the quick-start device comprises a first starting device and
a second starting device; the first starting device comprises a first
heating mechanism and a first gasification pipeline which winds on
the first heating mechanism; one end of the first gasification
pipeline is connected with the liquid storage container, and
methanol is conveyed into the first gasification pipeline through the
raw material conveyer and is heated and gasified by the first
heating mechanism; the hydrogen preparation equipment
comprises a reforming chamber; the second starting device comprises a second gasification pipeline, the main body of the second gasification pipeline is arranged in the reforming chamber, and the second gasification pipeline is heated while the reforming chamber is heated by the methanol output by the first gasification pipeline or/and the second gasification pipeline to ensure that the methanol in the second gasification pipeline is gasified. The system disclosed by the invention can be quickly started and is low in energy consumption and strong in practicability. However, the said procedure does not relate to our proposed startup method since it deals with the production of hydrogen from methanol and not the production of methanol itself from coal/ biomass.

[0012] The Indian patent application 201831017909
discloses a method to produce methanol from high ash coal by Oxyblown gasification. The said method utilized CO2 as a fluidizing medium along with steam and pure oxygen as the gasifying agent. However, the said invention does not provide any way to self-start a coal to methanol plant using CO2 in the Oxyblown mode or reduce the startup time.
[0013] Accordingly, there is a clear felt need in the art for
providing a simple, economical and efficient method for startup of a coal to methanol plant. The present invention meets the long-felt need.
OBJECTS OF THE INVETION
[0014] It is therefore the primary object of the present
invention to provide a methodology to produce CO2 using air blown gasification or coal combustion in bubbling fluidized bed gasifier followed by sulfur removal and CO2 capture to make available for oxy blown gasification used for methanol generation.
[0015] Another object of the present invention is to
utilize CO2 free syngas available from air blown mode gasification for the reduction of catalyst for the methanol reactor.
[0016] Yet another object of the present invention is to
provide an efficient method not only for starting of coal to methanol plant to reduce startup time but also to obliterate any requirement for using CO2 as an input, thereby designing a cost-effective solution.

SUMMARY OF THE INVENTION
[0017] A method for independent startup of coal to
methanol plant from high ash Indian coal comprising of the following steps of procedure: i) an air blown fluidized bed gasification of high ash Indian coal to generate syngas, ii) removal of sulfur from syngas, iii) removal and capture of CO2 from syngas for use in Oxyblown mode fluidized bed gasification of coal as the fluidizing medium, iv) Syngas utilized from airblown mode for methanol catalyst reduction for methanol production and save startup time, v) CO2 from air blown mode along with pure oxygen and steam used for Oxyblown fluidized bed gasification to produce syngas, vi) syngas so generated used for methanol production. The airblown fluidized bed can also be adapted to combustion mode for providing flue gas containing CO2. The CO2 generated is captured and supplied to the gasifier for the Oxyblown mode. The foregoing summary is illustrative only and is not intended to be in any way limiting.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0018] It is to be noted, however, that the appended drawings
illustrate only typical embodiments of the present subject matter
and are therefore not to be considered for limiting of its scope, for
the invention may admit to other equally effective embodiments.
The detailed description is described with reference to
accompanying figures. Some embodiments of system or methods in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to accompanying figures, in which:

[0019] Fig. 1 illustrates a process scheme to convert coal to
methanol.
[0020] Fig. 2 illustrates a process scheme of startup of coal to
methanol plant showing CO2 generation and catalyst regeneration.
[0021] Fig. 3 illustrates a process scheme of startup of coal to
methanol plant showing CO2 generation and catalyst regeneration wherein each subsystem has been shown in detail.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The method shown in Fig. 1 and Fig. 2 depicts
the scheme of starting and operation of the methanol plant. The process is operated under two modes of the fluidized bed gasifier, namely airblown mode and Oxyblown mode. The two modes of operation of the gasifier and integration into one process for self-reliant starting of the plant and overall time reduction is explained in detail in the following sections.
[0023] The process under airblown mode, the fluidized
bed adiabatic gasifier operating under bubbling fluidization regime where compressed air is introduced from the air separation unit (ASU) along with coal to generate syngas. The syngas generated under the airblown mode is passed through a sulfur removal system for removal of hydrogen sulfide. Thereafter, the sulfur free syngas is passed through a Water gas shift reactor and CO2 removal system where CO2 is captured. The syngas containing hydrogen (H2) and carbon monoxide (CO) is then sent to a methanol catalyst reactor for reduction of the

catalyst, which requires H2. The methanol reactor catalyst is either copper oxide or zinc oxide. The CO2 captured form the syngas generated under the airblown mode is stored in the CO2 storage tank for utilization in the Oxyblown mode.
[0024] The above stated approach starts up the
methanol plant to provide the fluidizing medium CO2 for the conversion of high ash coal to methanol under Oxyblown mode of the fluidized bed gasifier. The reduction of methanol catalysts by the syngas from the airblown mode makes them ready to produce methanol directly from the syngas available from the Oxyblown mode, thereby significantly reducing the overall time of startup of the plant.
[0025] In the subsequent sequence of operation, the
scheme is operated under the Oxyblown mode of the gasifier. During the Oxyblown mode, high ash coal, pure oxygen, steam and CO2 from the storage tank are introduced into the fluidized bed gasifier to produce syngas. The syngas thus produced is passed through the sulfur removal system to remove hydrogen sulfide. The syngas then passed through the Water gas shift reactor and CO2 removal system. Thereafter, the syngas is sent to the methanol synthesis system for the direct generation of methanol and collection. Pure CO2 available from the CO2 capture system is sent to the CO2 storage tank to be used as a continuous supply for the fluidized bed gasifier to continue operation in the Oxyblown mode.
[0026] In sum, the present invention outrightly omits the
requirement of CO2 in any step of method, thereby reducing the time for the overall reaction as well as reflecting a positive effect

on the cost component.
[0027] The following preferred embodiment seeks to clearly
explain the present invention while not limiting the scope of the invention.
[0028] Airblown mode of operation of fluidized bed gasifier
[0029] The fluidized bed adiabatic gasifier operating under
bubbling fluidization regime can be started with oxy blown mode using CO2 generated from air blown mode with the same gasifier earlier as shown if Figure 1.
[0030] In air blown mode, the fluidized bed gasifier is
operated with stoichiometric ratio of coal to air and gasification is carried out at 950°C and pressure in the range of 5-25 bars. The generated syngas has typical composition of 12 % H2, 18 % CO, 2 % CH4, 12 % CO2, 6-12 % H2O, 1500 ppm of H2S and balance N2. Air is supplied from compressor of ASU at 6 bar and 150°C into gasifier to carry out air blown gasification.
[0031] As shown in Fig. 2, syngas from gasifier system goes
to H2S removal system where H2S is removed using MDEA based absorption system. The outlet of H2S system contains of 12 % H2, 18 % CO, 2% CH4, 12 % CO2, 6-12 % H2O by volume with 0.1ppm of H2S and balance of Nitrogen.
[0032] From H2S removal system syngas goes to Water gas
shift reactor (WGSR), where syngas is contacted with water –gas shift catalysts (CoO/MoO based catalysts) at 350°C. Syngas is passed for about 6 hrs to carry out reduction of water gas shift reactor at 350°C. Once the temperature is stabilized at 350°C,

steam is injected at 350°C with steam to syngas ratio of 0.12. The syngas from water gas shift reactor has the composition of 24 % H2, 12 % of CO, 1 %CH4, 24 % CO2, 12-16 % H2O and balance N2 by percent volume, and temperature of 450°C.
[0033] The syngas from WGSR system is cooled to 40°C in
the cooler (CLR-301) as shown in Fig.3 and sent to CO2 capture system. The CO2 capture system consists of CO2 absorber and CO2 stripper as shown in Fig.2. Syngas from CLR-301 is contacted with 30 wt % MEA (Mono ethanolamine) solution with Syngas to MEA mass flow rate ratio of 5-7. 95 % of CO2 in the syngas is removed in the CO2 absorber and syngas from CO2 absorber is sent to Methanol reactor for reduction of methanol catalyst. The syngas composition going into methanol reactor for the catalyst reduction is 30-35 % H2, 16% CO, 2% CH4 and balance N2. The CO2 rich MEA solution from CO2 absorber is heated to 100°C in cross heat exchanger and sent to CO2 stripper.
[0034] In CO2 stripper MEA solution is heated using reboiler
at 110°C and stripped CO2 gas from solution is condensed and compressed. The Compressed CO2 gas is sent to CO2 tank for the storage and will be utilized in Oxyblown mode for methanol production.
[0035] Simultaneously 10-15% of syngas from CO2 absorber
is mixed with pure nitrogen in proportion of 1: 10 (Syngas: N2) and heated to 210°C and sent into the Methanol reactor. The balance of syngas is vented. The syngas reduces CuO/ZnO based catalyst at 210°C for about 24 hrs. During 24 hrs of reduction process, CO2 tank is filled with CO2. Once Methanol catalyst reduction is achieved, and CO2 tank is filled with CO2. The plant is

ready to shift to an Oxy blown mode for methanol production as Water gas shift reactor catalyst and methanol catalysts are in the reduced form.
[0036] Oxyblown mode of operation of fluidized bed gasifier
[0037] In Oxyblown mode, the air from ASU compressor is
fed into cryogenic separation unit having rectification column to produce O2 of 99% purity as shown in Fig.1. from where the oxygen is supplied to fluidized bed gasifier. The CO2 is supplied from CO2 tank which was filled during airblown mode of operation. The gasifier is started, and the fluidized bed gasifier is operated with stoichiometric ratio of coal to oxygen of 1, with pure CO2 as a fluidizing media and gasification is carried out at 950°C and pressure in the range of 5-25 bars. The generated syngas has typical composition of 12% H2, 24% CO, 2% CH4, 50-55 % CO2 and 6-12 % H2O by volume and 1500 ppm H2S.
[0038] The syngas from gasifier is cooled to 40°C and is fed
into H2S removal system where syngas is contacted with 30-50 wt % MDEA solution in H2S absorber (as shown in Fig.3). The syngas from H2S absorber has 0.1 ppm H2S and composition of 12 % H2, 24% CO, 2% CH4, 50-55% CO2 and 6-12% H2O by volume. H2S rich MDEA solution is heated to 100-120°C and fed into H2S stripper where H2S gas is stripped and vented.
[0039] From H2S removal system, syngas goes to Water gas
shift reactor (WGSR), where syngas is contacted with water –gas shift catalysts (CoO/MoO based catalysts) at 350°C. Steam is injected at 350°C with steam to syngas ratio of 0.12. The syngas from water gas shift reactor has the composition of 24% H2, 12% of CO, 1% CH4, 50-55% CO2, 12-16% H2O and balance N2 by

percent volume and temperature of 450°C.
[0040] The syngas from WGSR system is cooled to 40°C in a
cooler- CLR-301 (as shown in Fig.3) and sent to CO2 capture system. The CO2 capture system consists of CO2 absorber and CO2 stripper as shown in Fig.2. Syngas from CLR-301 is contacted with 30 wt % MEA (Mono ethanolamine) solution with Syngas to MEA mass flow rate ratio of 5-7. 95% of CO2 in the syngas is removed in the CO2 absorber and syngas from CO2 absorber is sent to Methanol reactor for methanol synthesis. The syngas composition going into methanol reactor for the methanol synthesis is 30-35 % H2, 16% CO, 2 % CH4 and balance N2. The CO2 rich MEA solution from CO2 absorber is heated to 100°C in cross heat exchanger and sent to CO2 stripper.
[0041] In CO2 stripper MEA solution is heated using reboiler
at 110°C and stripped CO2 gas from solution is condensed and compressed. The compressed CO2 gas is sent to CO2 tank for the storage and is recycled into gasifier.
[0042] Entire process for producing methanol under
Oxyblown mode from start-up takes only 5-6 hrs instead of 36-40 hrs, as time for WGS and Methanol catalyst reduction is saved.
[0043] The various aspects and schemes disclosed herein are
for purposes of illustration and are not intended to be limiting, with the true scope being indicated by the following claims.

We Claim:
1. A method of preparing methanol from coal using any
external carbon dioxide (CO2) by employing a gasifier in two different modes in a methanol plant, said method comprising the steps of:
i. feeding coal and compressed air to a fluidized bed gasifier operating in airblown mode at 950°C and pressure in the range of 5-25 bars;
ii. gasifying high ash Indian coal with 25-40% ash content for generating syngas, said syngas from gasifier system is fed to a H2S removal unit where H2S is removed using MDEA (Methyl diethanolamine) based absorption system;
iii. transferring syngas to water gas shift reactor (WGSR) where said syngas is passed for about 6 hours to carry out reduction of WGSR catalysts (CoO/MoO based catalysts) at 350°C along with steam;
iv. passing of conditioned syngas into a carbon dioxide (CO2) capture system after passing through a cooler to reduce the temperature of said syngas to 40°C, for removal of CO2 into mono ethanolamine solution (MEA), said conditioned syngas

from CO2 absorber is mixed with pure nitrogen in proportion of 1: 10 (Syngas: N2), heated to 210°C and sent into the methanol reactor for reduction of methanol catalyst;
v. reducing the methanol catalyst at 210°C for about 24 hours;
vi. heating the CO2 rich MEA solution from CO2 absorber 100°C in cross heat exchanger and transferring to CO2 stripper where it is heated using reboiler at 110°C, wherein stripped CO2 gas from solution is condensed, compressed and subsequently sent to CO2 tank for storage to be utilized in Oxyblown mode for methanol production.
vii. shifting the operation of the fluidized bed gasifier to Oxyblown mode for methanol production after 24 hours’ reduction process of methanol catalyst and storing CO2 in CO2 tank in the airblown mode,
characterized in that compressed air is used as gasifying agent in the airblown mode and pure oxygen is used as a gasifying agent in the Oxyblown mode of the gasifier.
2. The method of startup of coal to methanol plant as claimed
in claim 1, wherein CO2 obtained from the downstream process in the airblown mode of syngas generation is fed

back to said gasifier to act as readily available fluidizing medium in the oxyblown mode along with steam.
3. The method of startup of coal to methanol plant as claimed in claim 1, wherein the syngas generated under airblown mode is used to reduce water gas shift reactor catalyst and methanol catalyst simultaneously.
4. The method of startup of coal to methanol plant as claimed in claim 3, wherein the methanol catalyst is a Copper oxide or Zinc oxide based catalyst.
5. The method of startup of coal to methanol plant as claimed in claim 4, wherein the methanol catalyst in the reduced form, obtained during airblown gasification is used to produce methanol directly by reducing startup time of the plant by more than 36 hr.
6. The method of startup of coal to methanol plant as claimed in claim 1, wherein the air is supplied from compressor of air separation unit (ASU) at 6 bar and 150°C into gasifier to carry out airblown gasification.
7. The method of startup of coal to methanol plant as claimed in claim 1, wherein the steam is injected into the WGSR at 350°C and in the ratio, steam to syngas 0.12.

8. The method of startup of coal to methanol plant as claimed in claim 1, wherein the CO2 capture system removes about 95% of CO2 from syngas.
9. The method of startup of coal to methanol plant as claimed in claim 1, wherein 10-15% of syngas from the CO2 capture system is mixed with pure nitrogen in the ratio, 1: 10 (syngas: nitrogen), heated to 210°C and sent to the methanol reactor for catalyst reduction while the rest of the syngas is vented.