Waste to Hydrogen

Pathway to reliable and renewable clean energy future, H2-XERONOX®, a safe Thermal-chemical conversion process.

H2-XERONOX® process

The H2-XERONOX® systems rely on the harmonic resonance combustion (HRC) system, which is at the core of the process and supplies the necessary thermal heat. The HRC is integrated within the near oxygen-free reactor and produces superheated steam that acts as both the fluidizing and reaction agent. This process, known as a thermo-chemical conversion, converts carbon-based material into hydrogen-rich syngas. The reaction temperature is heavily influenced by the steam temperature and the biomass molar ratio of steam to carbon (STBR), which, in turn, strongly impacts the gas composition.

The H2-XERONOX® process for carbon-based feedstock to hydrogen comprises the following staged reactions:

The main reactions in pyrolysis and catalytic steam reforming of carbonaceous material are:   

Pyrolysis CxHyOz → H2O + H2 + CO + CO2 + tar + hydrocarbon volatiles + char

Tar reforming CxHyOz  + H2O → CO + H2

Hydrocarbon volatiles steam reforming CmHn + H2O → CO + H2

Catalytic cracking Tars -> H2O + H2 + CO + CO2 + CH4 + CmHn + CxHyOz

Tar dry (CO2) reforming  CxHyOz + CO2 → CO + H2

Hydrocarbon volatiles dry (CO2) reforming      CmHn+CO2 → CO+H2

Water gas shift CO + H2O → CO2 + H2

Char steam gasification C + H2O → CO + CO2 + H2

Char CO2 gasification  C + CO2 → 2CO

Whereas.

CxHyOz  Carbonaceous material 
CmHn     Hydrocarbons
C            Carbon 
H2             Hydrogen
H2O       Steam
O           Oxygen
CO        Carbon monoxide
CO2        Carbon dioxide            

Bio-mass pyrolysis

For calculation purposes, an empirical ‘mole’ of biomass will be regarded as

CH1.46 O0.67, (i.e., Carbon ~52.2%, Hydrogen ~6.1%, Oxygen ~41.7% on a mass basis.)

Primary: CH4 + H2O ↔ CO + 3H2  -206.3 kJ/mol.
Secondary: CH
4 + 2H2O ↔ CO2 +4H2  -165.kJ/mol.|
CO-steam reaction: CO + H
2O ↔ CO2 + H2  +40 kJ/mol.
Boudard reaction: C + CO
2 ↔ 2CO  -173.8kJ/mol.
Dry reforming: CH
4 + CO2 ↔ 2CO + H2O  -247.3kJ/mol.|
Methanisation: C + 2H
2 ↔ CH4  +74.82 kJ/mol.

The staged process given above shows the general chemical reactions taking place in a near oxygen-free reactor and in presence of steam. In the first stage, the carbon-based mass is thermally decomposed by steam to gases and residual char (carbon). The liberated gases consist primarily of higher hydrocarbons including tars, but these are immediately deteriorated due to high temperatures in the reactor. In the second stage, the excess steam reacts with the residual hydrocarbons and char producing synthesis gas (syngas is a mixture of hydrogen and carbon monoxide). The geometrical dimensions of the reactor provide additional residence time for near-total conversion. The gasification reactions that occur in the near oxygen-free environment are endothermic and the HRC provides all thermal energy required for this thermal conversion process. According to chemical equilibrium requirements, some CO2, and minor quantities of CH4 are also produced depending upon the specific feedstock and the gasifier operating conditions. 

H2-XERONOX® process is basically hydrogen combustion, heating and pyrolysis reactor infrastructure composed of four major components: the reactor, the HRC, heat exchangers with heat recovery units and PSA. Furthermore, there are cooling and scrubbing and feeding components as shown in the simplified flow sheet.

H2-XERONOX® process offers the technology to convert carbon-based mass to H2-rich synthesis gas which can be further separated and purified by pressure swing adsorption (PSA). It is noted that the steam pyrolysis process runs at safe atmospheric pressure; therefore, no elevated pressure is required.

The HRC unit of the H2-XERONOX® system is a thermoacoustic combustion and heating system that provide all thermal energy for the conversion process. The HRC is fuelled by the recycled hydrogen and the off-gas from the pressure swing adsorber.

The PSA technology is based on the physical binding of gas molecules to adsorbent material. The respective force acting between the gas molecules and the adsorbent material depends on the gas component, type of adsorbent material, partial pressure of the gas component and operating temperature. The separation effect is based on differences in binding forces to the adsorbent material. Highly volatile components with low polarities, such as hydrogen, are practically non-adsorbable as opposed to molecules such as N2, CO, CO2, hydrocarbons, and water vapour. Consequently, these impurities can be adsorbed from a hydrogen-containing syngas stream, and high-purity hydrogen is recovered.

Heat exchangers capture and recover heat from the high-temperature syngas and transfer this thermal energy to the steam generator; recycling the thermal energy drastically increases the system’s total thermal efficiency.

Thermodynamic Analysis on the Performance

Syngas composition analysis based on a mass and energy balance analysis using the chemical reactions as above and under thermal and chemical equilibrium conditions for the pyrolysis unit, Balu, E (2013) developed a mathematical model for predicting the synthesis compositions from superheated steam pyrolysis of biomass.

Using typical biomass with the chemical composition of CH1.46 O0.67 provides in Fig. 2. the molar fractions of gaseous species for dry syngas (water vapour and solid carbon are excluded in the molar fraction results) at three steam inlet temperatures. The molar fraction versus the steam to biomass molar ratio (STBR) results can be divided into three temperature zones, 800, 1000, and 1200°C. The STBR 0.1 – ~1.0 refers to the existence of a solid carbon deposit, and STBR ~1.0 – ~6.5 corresponds to no carbon deposit and CH4 production dropping down to zero. STBR 6.5 < starts when the molar fraction of CH4 reaches zero. After CH4 is no longer produced, there is no more carbon element left to sustain the increase in the production of CO, CO2, and that results in the condition of the so-called “saturated syngas composition” where the molar fractions of the gaseous species remain relatively constant and become independent of the STBR. Under the syngas composition equilibrium, the dry syngas would be composed of H2, CO, and CO2, and each component remains at a constant molar fraction.

System performance model

The system performance model is based on the following assumptions:

  1. The pyrolizer reactor is assumed to be perfectly insulated and in thermal and chemical equilibrium. The results given in Figure 2. are used for the performance analysis.
  2. The PSA separation is an ideal process to separate hydrogen with a purity of 99.999%, and all CO in the syngas is converted to H2 and CO2, and there is no more steam (H2O) available.
  3. The cooling heat exchanger and the surplus heat recovery unit are all ideal heat exchangers.
  4. The H2 combustor (HRC), with an integrated steam generator capable of producing superheated steam to a maximum of 1200 °C, is totally insulated and operates under the adiabatic flame temperature condition; no heat is lost.

Based on the above assumptions, the model that can predict the performance of the integrated system has been developed Chung (, 2014) using the conservation of mass and energy principles.

System performance evaluation

The performance evaluations for the system are based on 100 kg/h biomass feeding rate and steam to biomass ratio of 2 and 3; the STBR start from 1 as the formation of solid carbon, steam to biomass ratio <1 always means less efficient use of biomass resources.

Hydrogen combustion heat supply system

The net hydrogen production rate as a function of the STBR is shown in Figure 3. The net hydrogen production rate is a direct reflection of the syngas composition profile shown in Figure 2. In STBR 2, the H2 production rate increases with the STBR, while for a given STBR, a higher steam inlet temperature results in a higher H2 production rate. In STBR 3, both the STBR and steam inlet temperature make no difference in the composition as the system has reached the saturation condition due to the exhaustion of carbon elements. For the 100 kg/h biomass input rate, the maximum theoretical H2 production rate for biomass is around 13.2 kg/h.

Figures 4. and 5. provide the net CO2 and CH4 production rates, respectively. While the CO2 production rate follows the same trend as that of the H2 production, the CH4 displays a reversed trend where the higher the steam inlet temperature causes, the lower the CH4 production rate. The CH4 production rate also decreases with increasing STBR.

The water balance together with the H2 recycles ratio. Figures 6 and 7 give the information for the hydrogen recycling ratio which is defined as the amount of H2 taken back to the HRC system to facilitate the H2 combustion for steam generation to that of the total hydrogen produced. Figure 7 shows the rate of external ambient temperature water supplied. It should be made clear that the results given in Figures 6. and 7. are based on the principle of minimizing the ratio of recycled H2 or maximizing the net H2 production. In the 1000°C zone, as shown in Figure 6. this recycle ratio increases with the STBR, and for a given STBR, it is higher for a higher steam inlet temperature. However, with STBR 3, this ratio becomes independent of the STBR, and it increases slightly with increasing steam inlet temperature. Thus, the maximum H2 recycle ratio for the HRC is around 15%, but this figure will be lower with the utilization of the PSA tail gases.

The rate of external water for steam required is like that of the H2 production rate, and it maximizes around 60%.

The most useful parameter of performance evaluation is the efficiency of the system.

The cold gas and hot gas efficiencies are defined as follows solely for the gasifier.

The overall system efficiency is defined for the entire integrated system.

It is noted that the hydrogen combustion heat supply system is self-sustainable with hydrogen recirculation and the use of PSA tail gas.

The three efficiencies for the concept system are plotted in Figure 8. The cold gas efficiency starts at 78% for the STBR at unity and decreases monotonically with increasing STBR. For example, at the STBR of 10, the cold gas efficiency is down to 32%. The main reason that the cold gas efficiency drops at higher STBRs is that more energy is needed to heat the increasing amount of steam than the chemical energy gained. However, the hot gas efficiency that includes the thermal energy of the syngas is relatively insensitive to the change in STBR. The hot gas efficiency varies between 89 and 94%. It is also relatively constant on the overall system efficiency, with values ranging between 83 and 87%. Based on the values of the three different efficiencies, it can be summarized that the goal is to produce more hydrogen; the STBR should be kept at lower values.

Conclusion

  1. The high temperature near oxygen-free process uses superheated steam at >800°C – 1000°C to gasify the biomass feedstock. Almost all the carbon is converted to pure fuel gas. As a result, all the tars and char are broken down with almost no ash. The trace amounts of inorganic materials in the biomass are converted to inert vitreous slag, a non-hazardous, non-toxic by-product, with high environmental benefit for uses in the agricultural sector due to its ability to correct soil acidity.
  2. The hydrogen combustor, HRC in System that provides the superheated steam gasifying agent is a clean thermochemical process and draws the fuel from the H2 produced and the tail-gas from the PSA process (<20% of total H2 produced), so the system is self-sufficient, and there is no need for external heat supply.
  3. With a pressure swing adsorption, H2-XERONOX® can produce near pure hydrogen 99.999%.
  4. Biomass or carbonaceous energy brings numerous environmental and economic benefits – reducing air and water pollution, regional and rural economic development and employment, renewable energy and energy reliability and security.
  5. Due to the high-temperature thermochemical conversion, the selectivity of the feedstock is substantially increased. Other than agricultural and forest biomass, most Municipal Bio-solids Waste and plastics can be converted to clean and white hydrogen.
  6. Combined with pure hydrogen production, temperature Thermochemical Conversion with steam pyrolysis systems potentially possesses more than 80% in first law overall system thermodynamic efficiencies.
  7. This high-temperature thermal-chemical conversion process consolidates system components by providing complete tar cracking, reforming, and gas separation, thereby increasing the thermodynamic efficiency and reducing overall cost, making the H2-XERONOX® thermo-chemical conversion process technical and economically viable.
  8. For applications in the rural and farm infrastructure, we recognize that biomass is inherently dispersed and abundant, making the energy costs for harvesting and transporting them prohibitive unless the fuel processing plant is nearby. As the H2-XERONOX® system can be designed at various scales, establishing a network of mobile and distributed energy (DE) plants would be another advantage of H2-XERONOX® thermo-chemical conversion systems.
  9. It is worth noting that the most significant benefit of using superheated steam as the gasifying agent is the much higher production rate of hydrogen. In an air-blown autothermal partial combustion and partial gasification system, the molar ratio of H2 to CO is about unity while in the H2-XERONOX® superheated steam gasification system, this ratio is 14. The higher H2 production is facilitated by the water gas shift (WGS) reaction that converts CO and water to H2 and CO2.
  10. H2-XERONOX®technology for a sustainable and green energy future.

Hydrogen is a difficult product to handle in terms of logistics therefore we believe in decentralized solutions, for for hydrogen production. The company focus on small- to medium-scale solutions we see microgrids and de-centralized power generation happening right where fuel for the fuel cell is generation or needed, in places like remote areas and rural communities.

We have no intention of operating these systems by ourselves, we will engineer, build the systems, and possibly establish partnerships with waste disposal companies and give these companies the opportunity to become operators and be part of an ever-growing hydrogen economy.

Opportunity to get involved in the hydrogen economy Read more

For more information about the H2-XERONOX technology, please contact us.

A cleaner energy future Read more

References:

  • Australian  Institute of Bioengineering and Nanotechnology
  • University of Queensland
  • Balu, E (2013. A Study of Biomass
  • Chung J. Front. Energy Res. 2014
  • Lee U. Fig 2-8
H2-XERONOX® pilot plant

Thermo-chemical reactor 100kWte

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