ZEITMOP concept � A polygeneration system

							             ZEITMOP concept – A polygeneration system
                        for municipal energy demands

                                       Jan Gorski,
                 D.Sc., Assoc. Prof., Rzeszow University of Technology,
                    Dept. of Heat Engineering and Air Conditioning,
                         W. Pola No. 2, 35-959 Rzeszow, Poland


                                    Eugene Yantovski,
                          Prof. D.Sc., Independent Researcher,
                       Elsasstrasse 58, D-52068, Aachen,Germany




           Keywords: clean energy, combined CO2 cycles, energy supply systems


                                        Abstract
  The reduction of greenhouse gases (of which CO2 contributes over 60%) to stop global
warming is now a major priority of governments around the world. Alternative approach
described in the paper is concerned with the “clean energy” or “zero-emission” technologies.
An original concept of semi-closed ZEITMOP cycle is being developed. It can be compared
to other research initiatives such CES and ZENG [2-4], as a response to the well recognised
challenges. As an answer to the crucial question of reduction the GHG emissions we propose
[10] new zero emission fuel-fired power plants and boiler houses (“ZEITMOP Boiler & Air
Cooler” and “Zero Emission Membrane Smokeless Heating”). Zero-emission co-generation of
power and heat allows such plants to be located in densely populated areas close to the
consumer.



   1. Introduction

 The world is facing twin energy-related threats: that of not having adequate and secure
supplies of energy at affordable prices and that of environmental harm caused by consuming
too much of it. safeguarding energy supplies is once again at the top of the international
policy agenda. Yet the current pattern of energy supply carries the threat of severe and
irreversible environmental damage – including changes in global climate. Reconciling the
goals of energy security and environmental protection requires strong and coordinated
government action and public support.
 The need to curb the growth in fossil-energy demand, to increase geographic and fuel-
supply diversity and to mitigate climate-destabilising emissions is more urgent than ever.
Global primary energy demand in the Reference Scenario (IEA/WEO-2005) is projected to
increase by over one-half between now and 2030 – an average annual rate of 1.6%. Almost
half of the increase in global primary energy use goes to generating electricity and one-fifth to
meeting transport needs – almost entirely in the form of oilbased fuels.
 Global energy-related carbon-dioxide (CO2) emissions increase by 55% up to 2030, or
1.7% per year, in the Reference Scenario. They reach 40 gigatonnes in 2030, an increase of 14
Gt over the 2004 level. Power generation contributes half of the increase in global emissions
over the projection period. Emissions are projected to grow slightly faster than primary
energy demand – reversing the trend of the last two-and-a-half decades – because the average
carbon content of primary energy consumption increases [1].
 Despite efficiency gains, efforts at diversifying supply, RD&D expenditures and technology
advances, energy security and environmental concerns continue to be as much of an issue
today than they were 30 years ago, and in some respect more so. Not surprisingly, energy
projections reveal increasing energy demand and CO2 emissions in the short and medium-
term if actions are not taken to change that future. The availability of new energy conversion
technologies will be crucial for future economic development.
 Fossil-fuel-fired power plants have energy current densities typically about one hundred
times greater than renewable energy technologies. This simply means that they need much
less land to produce the same amount of power. The mass-media have always tended to lay
the blame for anthropogenic pollution, firmly at the door of widespread fossil fuel usage.
Often, one hears an appeal for a widespread ban on fossil fuel use. Fossil fuels, in themselves,
do not cause pollution. It is the way in which they are burned that is the problem. The desire
by so many for a carbon-free energy supply is understandable, but not very realistic in the
short term. Such a supply will be in the very distant future. The reality is that, over the next
few decades and beyond, fossil fuels will dominate the energy mix [1,2,10].
 An Annex to Kyoto Protocol has now been firmly accepted by all Eropean Union countries.
The release of greenhouse gases within the EU needs to be reduced by ~8 % in 2012 with
respect to the 1990 levels. Even radically improving energy efficiency and promoting
development and commercialisation of numerous renewable energy technologies will not
constitute adequate options in meeting CO2 stabilisation objectives. This is because renewable
technologies do not address the specific challenge of controlling emissions from the projected
increase in fossil fuel usage. The unavoidable conclusion is this. The ever-widening gap that
is emerging with time between CO2 stabilisation requirements and the projected increase in
fossil fuel usage, can only be filled by new, zero-emissions, fossil-fuel-based technologies.
Bringing zero emissions, fossil-fuel-flexible and highly efficient power generation
technologies into commercial use, is a critical task for the 21st century. In fact, the authors
firmly believe that the urgent development of such technologies constitutes the single most
important issue related to fossil fuel use today.


   2. Zero Emission Technology

    Zero emissions technology - bakgrounds and history

 The wording “zero emissions” is popularly applied to nuclear or renewable energy. In this
paper it refers to hydrocarbon fuel fired energy production that does not produce emissions.
The interest in fossil fuel fired, zero emission power plants (ZEPPs) has greatly increased
recently due to the growing awareness of the reality of climate change. In operation renewable
energies are carbon neutral and so present a favorable solution to the problem of greenhouse
gas emissions. Unfortunately renewable energy sources are currently underdeveloped in
comparison to fossil fuel based technologies and much work is required before such energy
sources will produce a major portion of our energy.
 It is simply understood, that applying so called oxy-fuel technology almost all typical
gaseous efluents in the classical air-fuel combustion systems are avoidable. The oxy-fuel
process, sometimes also referred to as O2/CO2 combustion, is characterized by the feed of
pure oxygen into the combustion chamber. In order to limit a very high flame temperature
during combustion with pure oxygen, extensive flue gas recirculation is necessary. This is as
it were the replacement of air nitrogen by recirculating flue gas which mainly consists of
CO2. In comparison with the conventional combustion in air atmosphere the flue gas volume
at boiler outlet amounts to about 30 % for the oxy-fuel process only. Hence, the following
components will be less space-consuming than in a conventional power plant. Within the flue
gas treatment process chain, water vapour, inert gases and harmful components like SOx have
to be removed by condensation, scrubbing and phase separation. The remaining flue gas (95%
CO2 purity) is dried and compressed and will then be ready for transportation and storage.
This technology has been growing up in many countries (ex. Vaterfall plant, Germany) and is
realy attractive from the economical point of view and ecology.
 The first known scheme of a fuel fired power unit without a flue stack, cogenerating power
and liquid carbon dioxide, is the subject of a Russian patent (1967) by Degtiarev and
Gribovsky [2]. It comprises an air separation unit (ASU) to produce oxygen, a combustion
system that burns clean fuel in a mixture of oxygen and recirculated CO2, turbine expansion,
liquid carbon dioxide deflection and capture. The idea of capturing CO2 from power plants
and injecting it underground in liquid form or in the great ocean depths, belongs to C.
Marchetti (1997). In 1991 Yantovski [2] gave a description of the zero emission power cycle
(GOOSTWEG) with steam recirculation to moderate combustion of fuel in pure oxygen,
combined with triple turbine expansion and CO2 deflection for sequestration. Some
comparable ideas, discussed in [2], were presented by Marchetti (1979), Jericha (1985), Pak
(1989), Mathieu (1994), Sundquist (2001), Andersen (2002) and Ausubel (2004). The history
of zero emission power generation systems and critical review of many ZEPP cycles has been
extensively described in the paper of Foy & Yantovski (2006).
 In the recent programs of leading energy supply institutions like DOE of USA (Vision 21),
Zero Emission Power Plant concept has achieved top priority. It is remarkable, that there
exists a sharp irreconcilable controversy on the scale and cause of global warming with many
doubts about whether or not large-scale investment in ZEPP technology is justified.
 In relation to ZEPP, what is happening in the practical area? The US is very active through
a company called Clean Energy Systems (CES) Inc.[2,4]. This company have already
assessed ZEPP economics using water recirculation, carried out extensive testing of a gas
generator and have built a small scale 5 MW demonstration plant in Kimberlina. In Norway,
Aker Co. (ZENG-CES) will soon build a ZEPP of 40 MW capacity with co-generation of
power and liquid carbon dioxide for oil recovery enhancement [3]. Also underway are
numerous projects of coalbed methane recovery using liquid CO2 [1]. The exhaustive
collection of essential information on ZEPP technology with CO2 sequestration, is collected
and coordinated by the IEA research group, headed by P. Freund in Cheltenham, UK.


   ZEITMOP cycle – basic concept and principal operation
 In recent years, much research has been focussed on non-cryogenic means of air separation:
ion-transport membranes (ITM), [7]. Advanced oxy-fuel combustion systems require the
membrane modules supporting the pressure and temperature conditions involved and ensuring
large mass-transport behavior in high temperatures. This method has been proposed as a
principal idea of the “Zero Emission Ion Transport Membrane Oxyfuel Power (ZEITMOP)
cycle concept.
 The schematic of the ZEITMOP cycle [6,8] is presented in Fig. 1. Ambient air enters
compressor S-Air. After compression, it is heated up to around 750–900 C in heat exchanger
HE1 by the flue gases exiting turbine T-PR. The hot pressurised air then enters the ITM
ceramic oxygen separator, which separates the air into a relatively high pressure oxygen-
depleted air stream and pure oxygen, the latter penetrating the membrane. The flow of swept
oxygen and forms an oxidizer for the fuel gas (methane compressed in S-CH4) entering
combustor CC. The hot pressurized oxygen-depleted air leaving ITM, is heating recirculated
CO2 stream in the regenerative heat exchanger HE3 and expanded in turbine T-Air before
being discharged to the atmosphere. The flue gas mixture of CO2 and H2O exiting combustion
chamber (at about 1200 – 1450 C) is expanded in the low pressure turbine T-PR before
being cooled in HE2, and C1. At the ambient temperature, the water in the flue gas mix is in
liquid form while the CO2 remains gaseous. The bulk of the water therefore, is deflected out
of the cycle in Sep.-H2O. Almost pure CO2 enters the multi-staged inter-cooled compressor
units S1/S2/S3, from where a fraction (some percents) of highly compressed (90-210 bars),
supercritical CO2 is deflected out of the cycle (CO2-out) to be sequestered. The major portion
of the CO2 is then heated in HE3 before being expanded in the high pressure turbine T-CO2,
down to 15-20 bar. The main part of recirculated CO2 stream enters the combustion chamber
CC in order to stabilize the allowable level of turbine inlet temperate (TIT) and necessary T-
PR turbine cooling demands. About 61% of total power produced in the turbines is consumed
by compressor units, but for example at the TIT= 12000C and maximum pressure in the cycle
p = 90 bars, a specific fuel (CH4) consumption is only 0.158 kg/kWh. It is about two times
smaller than in simple gas turbine cycle. The net useful power (production of electricity) will
be close to Nn = 14.5 MWe. Assuming LHV=50 MJ/kg for methane, the thermal efficiency of
the cycle is t = 45.5%, which is very attractive comparing to actual technology level.
 This cycle during past six years has been extensively analyzed, modifyied and optimized by
our research team [6,8,9]. The results of latest PC simulation of the cycle (in the ASPEN-Plus
v.11 environment), completly presented in [8,9] and cited above, have shown its promising
performance predictions. In reality, this cycle plays a rule of an alternative combined heat-
and-power generation system (CHP). For the mentioned case a great amount of low grade
heat (at 150-1700 C) can be extracted from the interstage cooling of cequencially compressed
CO2, see.Fig 1. (coolers C1, C2 and C3). It can be used for domestic central heating system
or other, technology purposes. The next step of cycle development is to find new applications
and integrate a combustion chamber with the ITM unit (as a complex chemical reactor).
   3. ZEITMOP cycle – New forms and applications

 In all competitive schemes special air separation units (ASU) are required to produce
oxygen for the subsequent oxy-fuel combustion process. As a rule the mature technology of
cryogenic air separation is used (Matiant, CES, AZEP, ZENG), [1-5].
 Thinking about the future technology challenges it will be possible to manufacture both the
high-productivity ITM units (see, for example: Air Products Inc.), and coupled ceramic &
membrane chemical reactors, see, Fig.2. This concept is now tested for the ZENG pilot power
plant [3] in Risavika (Norway).
 Apart of previously explained the ZEITMOP cycle base our research group started an
analysis of several modyfications of this concept. The main groups of its possible applications
are oriented onto the economy branches responsible for a sustainable development such [10]:
   -   transportation (Zero Emission Transport Engine and Zero Emission Aircraft Engine),
   -   heat supply systems (ZEITMOP Boiler & Air Cooler, Inegrated Membrane Smokeless
       Heater, Zero Emission Membrane Smokeless Heating),
   -   power generation & CHP systems (Auto Membrane Steam Turbine Without Exhaust
       Gases, Zero Emission Rankine Cycle with Separate / Integrated ITM Combustor).
 Some choosen examples in a succeeding part show their major structure, important elements
and advantages.


   Boiler house for heating & cooling
 The mixture of the many kinds of energy supply required in Europe is not dominated by
power (i.e. electricity), but by heating. Typical boiler houses are responsible for a very
significant portion of GHG emissions. The scheme shown in Fig. 1 can easily be converted to
poly-generation of heat, cold and power. However, in practice, boiler houses alone produce
the required heat. In an innovative concept of Yantovski et all. [10], a zero emissions boiler
house is proposed, as shown in Fig. 3. Such a boiler house can produce cold air as well and
uses the same ITM combustor (see: Fig. 2). It works as follows:
Ambient air enters compressor 1, and is heated in 3 before entering the feed side of ITM
combustor, 4. After flowing along the shell side (i.e. outside tubes) of the ITM combustor, the
air loses ~70 % of its oxygen content and is expanded in turbine 5 before being discharged to
the atmosphere without causing any environmental damage. Compressed gaseous fuel from 8
is mixed with recycled CO2 before entering permeate side (inside tubes) of the combustor, 4.
Temperature of the permeate side gases increases as a result of combustion which takes place
due to penetration of O2 through the tubes from the shell side. The hot gases are first cooled
in recuperator, 10, before giving up heat to the hot water system in 14 for space heating and
then to the hot water supply system, 13. Temperature of the water entering the hot water
system is equal to 10-15 C. The combustion products of CO2 and H2O are at a pressure of 5-
20 bars. Water is deflected in 12, while the gaseous CO2 is compressed up to at least 70 bars
in 11. Upon exiting 11, a fraction of the CO2 is deflected to be sequestered while the bulk
portion returns via recuperator 10 and turbine 9 to be mixed with the fuel before entering the
tube side of ITM combustor 4, thus completing the cycle. If local cooling is required, some air
exiting 1 can be deflected to the air cooler 6 where it is cooled to ambient temperature. This
air is than expanded in 7, lowering the air temperature for cooling purposes (in a hot clima).


   Zero Emissions Membrane Boiler Integrated With ITM Combustor
 In contrast to the ITM combustor shown in Fig. 2, which is similar to an ordinary shell-and-
tube heat exchanger, the scheme shown in Fig. 4, proposes to combine the boiler and ITM
combustor [10], by embedding boiler tubes inside a permeate side while accommodating fuel
flow and its oxidation. For the sake of clarity, only one boiler tube is depicted inside one ITM
tube, all encased by one shell tube. It forms only one module of the Membrane Boiler
(Memboiler). In practice, such a system should contain many modules. The cross-section of
the module shell might not be circular but square or hexagonal as depicted in Fig. 4. The
bundle of such hexagonal tubes with the boiler and membrane tubes inside, forms a
honeycomb structure.
When the fuel (CH4), is oxidised as a result of O2 diffusing through the ceramic membranes,
heat energy is generated. But this energy release does not result in increase in a flue gas
temperature. The heat is immediately absorbed through the walls of the boiler tubes by an
expanding steam. A tube in fact, works as a once-through boiler. As the rate of heat transfer
from the flue gases on a permeate side will greatly exceed the rate of heat transfer to the shell
side, some ribbons or baffles should be installed. The baffles might be helical shape so as to
increase a path-flow of the fuel and permeate gases. Increasing the path length will help to
complete the combustion of the fuel. A feed air system does not require a compressor. The hot
depleted air exhausted from the system might be used elsewhere. Carbon dioxide (total flow)
is de-watered, liquefied and sequestered or used (fizzy drinks production). If no power is
needed, the memboiler might be used for heating only (an easiest scheme to adopt for
demonstration purposes ITM combustor and ZEITMOP principle).
      4. Summary and conclusions

  Secure, reliable and affordable energy supplies are fundamental to economic stability
and development. The threat of disruptive climate change, the erosion of energy security and
the growing energy needs of the developing world all pose major challenges for energy
decision makers. They can only be met through innovation, the adoption of new cost-effective
technologies, and a better use of existing energy-efficient technologies.
  For zero- or reduced emission the process of gas separation is a great importance. CO2
capture and storage technologies (CCS) can significantly reduce CO2 emissions from power
generation, industry and production of synthetic fuels but do not answer on the all questions.
   More efficient technologies for fossil fuels combustion, including coal combustion are
already available or in an advanced stage of development. These include high-temperature
pulverised coal plants and integrated coal-gasification combined-cycle (IGCC).
       Zero-emission technologies could deliver an alternative for reducing of CO2 emissions
from the coal and hydrocarbon fuels and natural gas in all economy sectors within a 15-years
time horizon. One of the most promissible solutions is an application of semi-closed oxy-fuel
combustion systems, incorporating of air membrane separation units integrated with the
controlled atmosphere chemical reactors.
   Some individual elements of advanced clean energy systems have been developed, but
there is an urgent need for an integrated full-scale demonstration plant (Kimberlina and
ZENG projects).
         The ZEITMOP study showed its good performance and versatility, somewhere
exceeding comparable systems, actually tested in USA and EU countries. Within the
international research group organized by E. Yantovski (www.zeitmop.de ) some valuable
results and wide-spread spectrum of ZEITMOP cycle applications has been proposed. It is an
urgent time to extend this study and find some new partners within the actual 7 -th FP
framework programmes.


  References
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