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1. CO2 reuse technologies
Near-term CO2 demand for use in EOR will help to support the development of initial CCS demonstration projects in favourable locations. However, for any CO2 reuse technology to have the potential to materially accelerate CCS deployment in the longer term, it must have the potential to demand large quantities of CO2, e.g. on a scale commensurate with capture from power generation and other large industrial sources.
The following shortlist of ten CO2 reuse technologies could potentially meet this requirement: enhanced oil recovery (EOR), urea yield boosting, enhanced geothermal systems, polymer processing, algae cultivation, carbonate mineralisation, CO2 concrete curing, bauxite residue carbonation, CO2 as a feedstock for liquid fuel production, and enhanced coal bed methane.
There are already many industrial uses for CO2, with the current global ‘non-captive’ consumption estimated to be approximately 80Mtpa; comprising 25Mtpa in the liquid and solid form and the remainder in gaseous and supercritical form.1
This section endeavours to account for all of the existing and emerging CO2 reuse technologies and applications that utilise CO2 as a feedstock or directly to manufacture an end product, at the time of compiling this report. It is recognised that new and potentially ‘breakthrough’ technologies may be developed in the future.
This section also considers the current and future potential market size of both the existing and emerging CO2 reuse technologies in order to understand the long-term CO2 utilisation potential and to determine if quantities are likely to be commensurate with the emissions generated from power plants or other large industrial sources. The scale of CO2 utilisation will significantly affect the impact that these technologies may have in potentially accelerating the long-term uptake of CCS.
1.1 List and description of technologies
Table 1.1 and Table 1.2 represent a list of existing and emerging potential uses for CO2 respectively. These lists are current as at the time of compiling the report. Each may not be entirely exhaustive of all possible applications for CO2, but identifies established common uses, and in the case of future potential technologies, identifies those most publicised and that upon preliminary examination appear to be more than just a ’pie in the sky’ idea. As time progresses new technologies are likely to materialise and the emerging technologies identified are likely to be developed and advanced further than acknowledged within.
1Note this does not include the large ‘captive’ volumes of CO2 generated and subsequently consumed in the same industrial process, most notable urea production, which globally produces and then consumes an estimated 113Mtpa of CO2.
Table 1.1 Existing uses for CO2
|Existing uses||Brief description|
|Enhanced oil recovery (EOR)||CO2 is injected into depleted oil fields. The CO2 acts as a solvent that reduces the viscosity of the oil, enabling it to flow to the production well. Once production is complete, the CO2 can potentially be permanently stored in the reservoir.|
|Urea yield boosting (non-captive use only)2||When natural gas is used as the feedstock for urea production, surplus ammonia is usually produced. A typical surplus of ammonia may be 5 per cent to 10 per cent of total ammonia production.If additional CO2 can be obtained, this can be compressed and combined with the surplus ammonia to produce additional urea.A number of projects have been implemented to capture CO2 from ammonia reformer flue gas for injection into the urea production process.|
|Other oil and gas industry applications||CO2 is used as a fluid for the stimulation/fracturing of oil and gas wells. It is typically trucked to site and injected as liquid carrying propping agents (sand and other materials which prop open the pores of the rock to prevent closure after stimulation).|
|Beverage carbonation||Carbonation of beverages with high-purity CO2.|
|Wine making||CO2 is used as a seal gas to prevent oxidation of the wine during maturation. CO2 is also produced during the fermentation process, and it is already captured on-site for reuse for its inert gas properties.|
|Food processing, preservation and packaging||CO2 is used for various applications in the food industry, including cooling while grinding powders such as spices and as an inert atmosphere to prevent food spoilage.In packaging applications, CO2 is used in modified atmosphere packaging (MAP) with products such as cheese, poultry, snacks, produce and red meat, or in controlled atmosphere packaging (CAP), where food products are packaged in an atmosphere designed to extend shelf life.Carbon dioxide is commonly used in MAP and CAP because of its ability to inhibit growth of bacteria that cause spoilage.|
|Coffee decaffeination||Supercritical CO2 is used as the solvent for decaffeinating coffee. It is preferred due to its inert and non-toxic properties.|
|Pharmaceutical processes||Use of CO2 in the pharmaceutical industry may overlap with other uses identified, as it typically includes inerting, chemical synthesis, supercritical fluid extraction, product transportation at low temperature, and acidification of wastewater.80–90 per cent of material consumption by mass in the pharmaceutical industry is attributable to solvent consumption. US pharmaceutical solvent consumption in 1995 was $$$∼80,000tpa, but supercritical CO2 was not used in significant enough quantities to be reported.|
|Horticulture||CO2 is provided to greenhouses to maintain optimal CO2 concentration and maximise plant growth rate. Sources include on-site cogeneration schemes as well as off-site industrial sources connected via pipeline networks.|
|Pulp and paper processing||CO2 is used to reduce pH during pulp washing operations.|
|Water treatment||CO2 is used for re-mineralisation of water following reverse osmosis and for pH control (reduction).|
|Inerting||CO2 is used in a wide range of applications where the physical properties of an inert gas are desirable. This includes applications covered under other use categories, such as a welding shielding gas and gas used in food packaging and in wine production.|
|Steel manufacture||CO2 is used in a minority of basic oxygen furnaces as a bottom stirring agent. It is also used for dust suppression.|
|Metal working||Used for varied purposes, including chilling parts for shrink fitting, and hardening of sand cores and moulds.|
|Supercritical CO2 as a solvent||CO2 is useful for high-pressure extraction and as a solvent to isolate targeted compounds, such as fragrances and flavours.Because of its low critical temperature and moderate pressure requirements, natural substances can be treated particularly gently. It is gaining favour as a solvent in the dry cleaning industry for this reason.|
|Electronics||Printed circuit board manufacture uses small quantities of CO2 in niche applications, predominantly as a cleaning fluid.|
|Pneumatics||Pneumatic applications for CO2 include use as a portable power source for pneumatic hand tools and equipment, as well as a power source for paintball guns and other recreational equipment.|
|Welding||Used as a shrouding gas to prevent oxidation of the weld metal.|
|Refrigerant gas||CO2 is used as the working fluid in refrigeration plant, particularly for larger industrial air conditioning and refrigeration systems. It replaces more toxic refrigerant gases that also have much greater global warming potential.|
|Fire suppression technology||When applied to a fire, CO2 provides a heavy blanket of gas that reduces the oxygen level to a point where combustion cannot occur. CO2 is used in fire extinguishers, as well as in industrial fire protection systems.|
2 Unless otherwise stated, all references made to urea production within the report refer to the incremental additional production of urea from surplus ammonia and non-captive CO2, e.g. the supply of CO2 from a source external to the process, not generated and subsequently used within the process itself.
Table 1.2 Emerging uses for CO2
|Existing uses||Brief description|
|Enhanced coal bed methane recovery (ECBM)||In CO2-ECBM, CO2 is injected into coal seams, where it preferentially adsorbs onto the coal, displacing and releasing adsorbed methane, which can then be recovered at the surface. A key constraint on practical application of this concept has been the decrease in permeability and injectivity that accompanies CO2 induced swelling of the coal.Nitrogen (N2) can also be used for ECBM, but it utilises a different mechanism, by reducing the partial pressure of the gaseous methane. This has led to the consideration of direct flue-gas injection for CO2, which would utilise both the mechanisms of CO2 and N2-ECBM.|
|Enhanced geothermal systems (EGS) − CO2 as a working fluid||There are two ways in which supercritical CO2 may be utilised in EGS geothermal power generation.Firstly, it may be used as the circulating heat exchange fluid. The benefit here is that the significant density difference between the cold CO2 flowing down the injection well(s) and the hot CO2 flowing up the production well(s) would eliminate the need for a circulation pump.Secondly, this concept could be extended, and the circulating CO2 could also be used directly as the working fluid in a supercritical CO2 power cycle. There is significant interest in supercritical CO2 power cycles because of the potential for high efficiency and compact turbo machinery.|
|Power generation − CO2 as a working fluid||Supercritical CO2 power cycles need not be limited to geothermal power plants, as the benefits of high efficiency and compact turbo machinery are not heat source-specific.The nuclear power industry is particularly interested in supercritical CO2 power cycles for this reason.|
|Polymer processing||One example of CO2 as a feedstock for polymer processing involves the transformation of carbon dioxide into polycarbonates using proprietary zinc based catalyst system. A variety of other process routes and end products have been proposed.|
|Chemical synthesis (excludes polymers and liquid fuels/hydrocarbons)||Carbon and oxygen are both key elements in organic chemistry. Consequently, there are a wide range of chemicals that can at least theoretically utilise CO2 as a feedstock for production, including organic acids, alcohols, esters, and sugars.The practicality of CO2 as a feedstock will vary significantly based on the current production routes.The dominant potential demand, based on current markets, could come from acetic acid, which has a current global market of ∼6Mtpa. Acetic acid can be produced by direct catalysis of CO2 and methane.|
|Algal bio-fixation||The productivity of algal cultivation systems can be increased significantly (up to a saturation point) by the injection/addition of CO2 to the growth medium/solution.|
|Calcium carbonate and magnesium carbonate||Mildly concentrated CO2 (e.g. power station flue gas) is contacted with mineral-loaded alkaline brine. The CO2 present in the gas precipitates out as mineral carbonates (limestone / dolomite equivalent precipitates). The resulting product can be further processed to form an aggregate equivalent product for the construction industry, and can also potentially displace a small portion of Portland Cement in concrete.|
|Baking soda (sodium bicarbonate)||This is a variant of mineralisation wherein CO2 is contacted with sodium rich brine, resulting in the formation of sodium bi-carbonate (NaHCO3).|
|CO2 concrete curing||This technology is focused on precast concrete production facilities, where the waste CO2 from onsite flue gas is permanently stored as un-reactive limestone within the concrete. This also limits the need for heat and steam in the curing process.The result is a reduction in emissions of CO2 equivalent to up to 120kg of CO2 per tonne (286 lbs CO2 per US ton) of precast concrete.|
|Bauxite residue treatment (‘red mud’)||The extraction of alumina from bauxite ore results in a highly alkaline bauxite residue slurry known as ‘red mud’. Concentrated CO2 can be injected into the red mud slurry to partially neutralise the product, improving its manageability, reducing its disposal costs and limiting its potential environmental impacts. In the neutralisation process, the CO2 is converted to mineral form (typically carbonates).The resulting product remains slightly alkaline, and has potential as a soil amendment for acidic soils.|
|Renewable methanol||Electrolysis of water produces H2. The H2 is combined with captured CO2, compressed and reacted over a catalyst at moderate temperature and pressure (∼5MPa, ∼225°C) to produce methanol and water.|
|Formic acid||Electro-reduction of CO2 to produce formic acid (HCOOH) and O2. Formic acid is used as a hydrogen carrier, with hydrogen the primary fuel. Formic acid has been classified as a liquid fuel as hydrogen is only released from the liquid formic acid as required.|
|Genetically engineered micro-organisms for direct fuel secretion||Engineered product-specific photosynthetic organisms circulate in a solution of micronutrients and brackish water, producing hydrocarbon products as a by-product of metabolism. Energy input is direct, un-concentrated solar energy.|
|CO2 injection to conventional methanol synthesis||The yield of methanol from conventional methanol synthesis can be increased (some estimates suggest up to a 20 per cent yield increase) by the injection of additional CO2 upstream of the methanol reformer.Industry consensus is that new plants will generally have an autothermal reformer, which tends to produce an excess of hydrogen such that CO2 injection will not be required.|
It should be noted that reliable and detailed end-use statistics on CO2 production and consumption are not readily available for many of the specific application, so the figures provided in Table 1.3 and Table 1.4 are indicative and provide an indication of the order of magnitude of the current CO2 consumption and potential future CO2 utilisation.
Consequently, these estimates are only considered ‘order of magnitude’ estimates. The specific values have not been presented herein, rather the range within which the demand of any given application is thought to fall is selected from the following standard set of demand ranges:
- Demand < 1Mtpa
- 1Mtpa < demand < 5Mtpa
- 5Mtpa < demand < 30Mtpa
- 30Mtpa < demand < 300Mtpa
- demand >300Mtpa
Table 1.3 Current and future potential CO2 demand of existing uses
|Existing uses||Current non-captive CO2 demand (Mtpa)||Future potential non-captive CO2 demand (Mtpa)|
|Enhanced oil recovery (EOR)||30< demand < 300||30< demand < 300|
|Urea yield boosting||5 < demand < 30||5 < demand < 30|
|Other oil and gas industry applications||1< demand <5||1< demand <5|
|Food processing, preservation and packaging*||∼8.5||∼15|
|Coffee decaffeination||unknown||1<demand <5|
|Horticulture||<1||1< demand <5|
|Pulp and paper processing||<1||<1|
|Water treatment||1 < demand < 5||1 < demand < 5|
|Supercritical CO2 as a solvent||<1||<1|
|Fire suppression technology||<1||<1|
*Actual estimates provided for beverage carbonation and food processing and packaging, as reasonable information is available for these uses
Table 1.4 Future potential CO2 demand of emerging uses
|Emerging uses||Future potential non-captive CO2 demand (Mtpa)|
|Enhanced coal bed methane recovery (ECBM)||30 <demand <300|
|Enhanced geothermal systems − CO2 as a heat exchange fluid||5< demand <30|
|Power generation − CO2 as a power cycle working fluid||<1|
|Polymer processing||5< demand <30|
|Chemical synthesis (excludes polymers and liquid fuels/ hydrocarbons)||1< demand <5|
|Calcium carbonate and magnesium carbonate||>300|
|Baking soda (sodium bicarbonate)||<1|
|CO2 concrete curing||30< demand <300|
|Bauxite residue treatment (‘red mud’)||5 < demand < 30|
|Genetically engineered micro-organisms for direct fuel secretion||>300|
|CO2 injection to conventional methanol synthesis||1< demand <5|
The ‘order of magnitude’ is very pertinent to the discussion on CO2 reuse, as there is a significant discrepancy in scale between current industrial CO2 consumption and CO2 capture quantities from a commercial-scale CCS plant. For example, a single 300MW (net) CCS demonstration project may capture approximately 2.5Mtpa of CO2. This single 300MW (net) demonstration project represents a rate of CO2 production that is greater than the current non-captive industrial consumption of Japan, South Korea and Australia combined.
1.2 First cut of technologies for detailed investigation and evaluation
A threshold of 5Mtpa global CO2 reuse potential was applied to the list of reuse technologies to focus the report on applications with large-market potential. The CO2 utilisation potential should be of a scale commensurate with future CO2 capture requirements from power generation and other large industrial sources.
Table 1.1 and Table 1.2 identify numerous options for the use of CO2. However, it is evident in Table 1.3 and Table 1.4 that many of the reuse applications and technologies have a limited demand and in the context of CO2 volumes associated with CCS plants, the demand is immaterial. While localised CO2 demand for EOR can make an important contribution to the development of early CCS demonstration projects, for a reuse technology to have any other material impact on accelerating the long-term uptake of CCS, the CO2 utilisation potential of the technology should be of a scale commensurate with CO2 capture from power generation and other large industrial sources.
To permit a more comprehensive study on those technologies which have the most potential, a threshold of 5Mtpa global CO2 reuse potential was applied. On this basis, the technologies short-listed for further analysis and evaluation are as follows:
- CO2 enhanced oil recovery;
- CO2 as a feedstock for urea yield boosting;
- Enhanced geothermal systems (using CO2 as a working fluid);
- CO2 as a feedstock in polymer processing;
- Algae production;
- Mineralisation (including carbonate mineralisation / concrete curing / bauxite residue carbonation);
- Liquid fuels (including renewable methanol / formic acid); and
- CO2 enhanced coal bed methane (ECBM) recovery.
Any CO2 reuse application with a market potential below the 5Mtpa threshold will not be investigated further as its size is immaterial in the context of CCS.
One exception that should be noted in relation to the above shortlist is that beverage carbonation and food processing and packaging as both have current global consumption levels of CO2 in excess of 5Mtpa. However, they are mature industries with an established supply chain, and with more modest growth rates expected into the future, the incremental demand for each will not necessarily ever exceed 5Mtpa, certainly not in the near term. For this reason, these reuse applications were excluded from the shortlist.
Another technology not explicitly listed above is CO2 enhanced gas recovery (EGR), which is distinct from ECBM. Please refer to section 2.1 for a brief discussion on EGR, and how it has been treated for the purposes of this study.