1. Background
In addition to its position as the world’s most abundant energy reserve, coal is used as an important primary energy source due to its economic advantages as well. Future consumption is expected to increase with economic growth as well as an increasing population. Meanwhile, in response to global warming caused by CO2, there is an earnest need to develop technology to use coal cleanly and more efficiently. In response, a process called HyPr-RING that enables the hydrogen necessary for future hydrogen-energy communities to be produced from coal is now under development for commercialization.
2. Theory of HyPr-RING process
HyPr-RING is a process in which a CO2-sorbent, CaO, is directly added into a coal gasifier and the CO2 generated by coal gasification is fixed as CaCO3, together with the produced hydrogen. The reaction between CaO and H2O produces the heat necessary for subsequent coal gasification in the gasifier. Within the gasifier, a series of reactions from equation (1) to equation (4) and the overall reaction of equation (5) take place.
This overall reaction is an exothermic reaction with C, H2O, and CaO as initial reactants. This means that, in theory, there is no need for external heat. It was also discovered that CO2 fixation enhances reactions (2) and (3) for H2 generation. Figure 1 shows the process concept of HyPr-RING. CaCO3 is regenerated by calcination into CaO for its recycle as a sorbent. Most of the heat energy required for calcination is carried as the chemical energy of CaO and made available for coal gasification to produce H2 in the gasifier.
How is this different from conventional gasification? Conventional gasification secures the heat necessary for gasification through a partial combustion of coal, with a reaction taking place in the gasifier expressed by the following equation:
Fig. 1 Concept of HyPr-RING process
Gasification gas must be sent through a low-temperature shifter and then exposed to a low-temperature absorbent such as amine for CO2 separation. At that time, the amount of CO2 gas separated is one mole per mole of hydrogen.
On the other hand, the HyPr-RING process uses dry CaO to absorb CO2 in the furnace (650°C, 30 atm). In this case, heat is released during CO2 absorption to maintain a high temperature in the gasifier.
Here, post-CO2 absorption CaCO3 is returned to CaO by calcination (reproduction) and, at that time, 50-80% of the thermal energy required is converted into CaO for reuse in the gasifier (Fig. 2).
As seen from equation (5), 2-mole hydrogen production from one mole of carbon is another important feature.
Fig. 2 Hydrogen production using HyPr-RING process
Table 1 CO2 separation energy and temperature level
3. Characteristics of HyPr-RING process
Cold gas efficiency
The HyPr-RING process gasifies the easy-to-gasify portion of coal under low-temperature (600-700°C) conditions into hydrogen and uses the remaining difficult-to-react char as fuel for CaCO3 calcination.
Figure 3 shows an example of a HyPr-RING process configuration with a fluidized-bed gasifier and an internal combustion-type calcining furnace. For product gas composition of 95% H2 and 5% CH4, the cold gas efficiency proved to be about 0.76.
CaO absorbent
At the gasifier inlet, where the temperature is low, CaO first reacts with H2O to produce Ca(OH)2, providing heat-to-coal pyrolysis. Then, at a high-CO2 partial pressure region, Ca(OH)2 absorbs CO2 to produce CaCO3, and releases heat. This heat is used for the gasification of char. To prevent CaO from becoming less active due to high-temperature sintering, a method of absorbing CO2 in the furnace, by way of Ca(OH)2, is employed. Gasification at a temperature as low as possible is also employed to prevent the eutectic melting of calcium minerals. In such cases, unreacted product carbon can be used as a heat source for CaO reproduction.
4. Project overview
Under this project, which commenced in 2000, process configuration identification and FS through testing with batch/semi-continuous equipment were paralleled with a variety of factor tests required. In and after FY2003, it is expected that 50-kg/day (coal base) continuous test equipment will be fabricated for continuous testing and then, based on the results, running tests and a FS of a 5 ton/day-scale pilot plant are to be carried out in and after 2006 to establish a commercialization process. Table 2 shows development targets of the project and Table 3 shows, the project timetable.
Table 3 Development timetable
Table 2 Targets
References
1) Shiying Lin, Yoshizo Suzuki & Hiroyuki Hatano, Patent No. 29791-49, 1999.
Energy Technology and the Environment, Editors: A. Bisio and S. Boots, John Wiley & Sons, New York, 1995
Source: New Energy and Industrial Technology Development Organization (NEDO), Japan Coal Energy Center (JCOAL)
The 10 largest coal producers and exporters in Indonesia:
