吸收式热泵在燃气采暖冷凝热回收中的应用

作者建立了一种利用吸收式热泵回收燃气锅炉冷凝热的系统，解决了供热回水温度高而难以回收烟气冷凝热问题，比现有的锅炉烟气冷凝热回收技术提高效率5％以上。计算分析结果表明，这一工艺的应用可产生显著的经济、节能和环保效益。     

Energy saving analysis and thermal performance evaluation of a hydrogen-enriched natural gas-fired condensing boiler

Hydrogen-enriched natural gas (HENG) has attracted widespread attention due to its lower pollutant emissions and industrial decarbonization in the past decades. HENG combustion boosts the water content in the flue gas, which is highly favorable for condensing boilers to recover additional latent heat. The energy saving and thermal performance of a condensing boiler burning HENG were evaluated at a constant heat load of 2.8 MW in this study. The variations in combustion products and boiler efficiency were investigated based on the material balance and energy conservation. The heat transfer calculations were employed to evaluate the thermal performance of boiler heating surfaces. The energy recovery performance of the condenser was assessed via a thermal design method. Results show that H₂ enrichment enhances the radiation intensity of the flame due to the incremental triatomic gases with higher emissivity in the furnace. The heat absorption ratio increases with H₂ enrichment in the radiative heating surface, while it shows a reverse tendency in the convective heating surface. The condensing boiler efficiency based on lower heating value increases from 101.83% to 110.60%, the total heat transfer rate of the condenser increases from 2.77 × 10⁵ W to 4.61 × 10⁵ W, and the total area required decreases from 46.45 m² to 42.16 m², as the H₂ enriches from 0 to 100% under the exhaust flue gas temperature of 318 K. Although the amount of recoverable heat in the exhaust flue gas increases considerably after H₂ blending, the original condenser with natural gas as the designed fuel could meet the requirements of the heat recovery for HENG without increasing the extra heating surface. When the H₂ fraction is enriched from 0 to 100%, CO₂ emission intensity drops from 6.05 × 10⁻⁸ kg J⁻¹ to 0. This work may offer some theoretical references for the application and generalization of HENG condensing boilers.     

Energy efficiency measures and conversion of fossil fuel boiler systems in a detached house

There is a large potential to reduce primary energy use and CO₂ emissions from the Swedish building stock. Here detached houses heated by oil, natural gas or electric boilers were assessed. CO₂ emissions, primary energy use and heating costs were evaluated before and after implementing house envelope measures, conversions to more efficient heating systems and changes to biomass fuel use. The study included full energy chains, from natural resources to usable heat in the houses. The aim was to evaluate the societal economic cost effectiveness of reducing CO₂ emission and primary energy use by different combinations of changes. The results demonstrated that for a house using an electric boiler, a conversion to a heat pump combined with house envelope measures could be cost efficient from a societal economic perspective. If the electricity was based on biomass, the primary energy use was at the same time reduced by 70% and the CO₂ emission by 97%. Large emission reductions were also seen for conversions from oil and gas boilers to a biomass-based system. However, for these conversions the heating cost increased, leading to a mitigation cost of around €50/tonne C avoided. The price of oil and natural gas greatly influenced the competitiveness of the alternatives. House envelope measures were more cost-effective for houses with electric boilers as the cost of energy for this system is high. The results are specific to a Swedish context, but also give an indication of the potential in other regions, such as northern European and large parts of North America, which have both a cold climate and a widespread use of domestic boilers.     

Condensing boiler applications in the process industry

Major challenging issues such as climate change, energy prices and fuel security have focussed the attention of process industries on their energy efficiency and opportunities for improvement. The main objective of this research study was to investigate technologies needed to exploit the large amount of low grade heat available from a flue gas condensing system through industrial condensing boilers. The technology and application of industrial condensing boilers in various heating systems were extensively reviewed. As the condensers require site-specific engineering design, a case study was carried out to investigate the feasibility (technically and economically) of applying condensing boilers in a large scale district heating system (40 MW). The study showed that by recovering the latent heat of water vapour in the flue gas through condensing boilers, the whole heating system could achieve significantly higher efficiency levels than conventional boilers. In addition to waste heat recovery, condensing boilers can also be optimised for emission abatement, especially for particle removal. Two technical barriers for the condensing boiler application are corrosion and return water temperatures. Highly corrosion-resistant material is required for condensing boiler manufacture. The thermal design of a “case study” single pass shell-and-tube condensing heat exchanger/condenser showed that a considerable amount of thermal resistance was on the shell-side. Based on the case study calculations, approximately 4900 m² of total heat transfer area was required, if stainless steel was used as a construction material. If the heat transfer area was made of carbon steel, then polypropylene could be used as the corrosion-resistant coating material outside the tubes. The addition of polypropylene coating increased the tube wall thermal resistance, hence the required heat transfer area was approximately 5800 m². Net Present Value (NPV) calculations showed that the choice of a carbon steel condenser ensured cash return in a relatively shorter period of time (i.e. 2 years) when compared to a stainless steel condenser (i.e. 5-7 years). Moreover, the NPV for the stainless steel was more sensitive to the change of the interest rate.     

A comparison of electricity and hydrogen production systems with CO2 capture and storage. Part A: Review and selection of promising conversion and capture technologies

We performed a consistent comparison of state-of-the-art and advanced electricity and hydrogen production technologies with CO₂ capture using coal and natural gas, inspired by the large number of studies, of which the results can in fact not be compared due to specific assumptions made. After literature review, a standardisation and selection exercise has been performed to get figures on conversion efficiency, energy production costs and CO₂ avoidance costs of different technologies, the main parameters for comparison. On the short term, electricity can be produced with 85–90% CO₂ capture by means of NGCC and PC with chemical absorption and IGCC with physical absorption at 4.7–6.9 €ct/kWh, assuming a coal and natural gas price of 1.7 and 4.7 €/GJ. CO₂ avoidance costs are between 15 and 50 €/t CO₂ for IGCC and NGCC, respectively. On the longer term, both improvements in existing conversion and capture technologies are foreseen as well as new power cycles integrating advanced turbines, fuel cells and novel (high-temperature) separation technologies. Electricity production costs might be reduced to 4.5–5.3 €ct/kWh with advanced technologies. However, no clear ranking can be made due to large uncertainties pertaining to investment and O&M costs. Hydrogen production is more attractive for low-cost CO₂ capture than electricity production. Costs of large-scale hydrogen production by means of steam methane reforming and coal gasification with CO₂ capture from the shifted syngas are estimated at 9.5 and 7 €/GJ, respectively. Advanced autothermal reforming and coal gasification deploying ion transport membranes might further reduce production costs to 8.1 and 6.4 €/GJ. Membrane reformers enable small-scale hydrogen production at nearly 17 €/GJ with relatively low-cost CO₂ capture.     

Technical,economic, and environmental analyses of the modernization of a chamber furnace operating on natural gas or hydrogen

The paper presents a technical, economic and environmental analyses of a chamber furnace used to heat the charge before forging. The energy efficiency of the furnace before the modernization was 18%, after the modernization it was 31% (partial modernization due to large financial outlays). Other variants were also analysed: complete modernization, the variant of furnace modernization with 30% hydrogen content in the gas and the variant with 100% hydrogen as fuel. The analyses showed that with the current gas price (0.025 EUR/kWh) and the price of emission allowances (nearly 60 EUR/MgCO₂) and 100 cycles/year, the difference in Net Present Value (NPV) before base variant and partial modernization is around 900,000 EUR and before base variant and full modernization is 1,200,000 EUR. The introduction of the gas and 30% of hydrogen co-combustion option versus the base scenario option for 150 cycles per year results in a NPV difference of at least 2 million EUR. The option of 100% hydrogen as a fuel is the most advantageous from the point of view of reducing CO₂ emissions - it is largely influenced by the rising prices of CO₂ emission allowances.     

A liquefied energy chain for transport and utilization of natural gas for power production with CO2 capture and storage – Part 2: The offshore and the onshore processes

A novel energy and cost effective transport chain for stranded natural gas utilized for power production with CO₂ capture and storage is developed. It includes an offshore section, a combined gas carrier, and an integrated receiving terminal. In the offshore process, natural gas (NG) is liquefied to LNG by liquid carbon dioxide (LCO₂) and liquid inert nitrogen (LIN), which are used as cold carriers. The offshore process is self-supported with power, hot and cold utilities and can operate with little rotating equipment and without flammable refrigerants. In the onshore process, the cryogenic exergy in LNG is used to cool and liquefy the cold carriers, which reduces the power requirement to 319 kWh/tonne LNG. Pinch and exergy analyses are used to determine thermodynamically optimized offshore and onshore processes with exergy efficiencies of 87% and 71%, respectively. There are very low emissions from the processes. The estimated specific costs for the offshore and onshore process are 8.0 and 14.6 EUR per tonne LNG, respectively, excluding energy costs. With an electricity price of 100 EUR per MWh, the specific cost of energy in the onshore process is 31.9 EUR per tonne LNG.     

Role of energy efficiency standards in reducing CO2 emissions in Germany: An assessment with TIMES

Energy efficiency is widely viewed as an important element of energy and environmental policy. Applying the TIMES model, this paper examines the impacts of additional efficiency improvement measures (as prescribed by the ACROPOLIS project) over the baseline, at the level of individual sectors level as well as in a combined implementation, on the German energy system in terms of energy savings, technological development, emissions and costs. Implementing efficiency measures in all sectors together, CO₂ reduction is possible through substitution of conventional gas or oil boilers by condensing gas boilers especially in single family houses, shifting from petrol to diesel vehicles in private transport, increased use of electric vehicles, gas combined cycle power plants and CHP (combined heat and power production) etc. At a sectoral level, the residential sector offers double benefits of CO₂ reduction and cost savings. In the transport sector, on the other hand, CO₂ reduction is the most expensive, using bio-fuels and methanol to achieve the efficiency targets.     

分离式冷凝型天然气锅炉的研究与应用

介绍了常用冷凝型锅炉结构,重点讨论了分离式冷凝锅炉的特点,实验研究了以空气和水为冷却介质的烟气冷凝换热的规律,常规锅炉与烟气冷凝热能回收装置构成的冷凝锅炉系统的工程应用获得了满意的结果,节能与环保效益显著。     

具有混合气体冷凝的燃气锅炉系统

介绍了常用的冷凝型锅炉结构,重点讨论分离式冷凝锅炉的特点。天然气锅炉烟气中含有相当比列水蒸汽,携带大量汽化潜热,与燃煤锅炉明显不同,提供了更大的余热利用空间。针对燃天然气热水锅炉,研制开发了采用烟气冷凝热能回收装置的锅炉系统并应用于实际。运行测试表明,改造的锅炉运行正常,提高锅炉热效率5%以上,节约大量天然气,同时吸收烟气中部分NOx,起到一定净化作用。本系统投资回收期短,节能与环保效益显著。     

Actual heating energy savings in thermally renovated Dutch dwellings

The register of the Dutch social housing stock was analysed, containing 300.000 dwellings, renovated between 2010 and 2013. The main objective was twofold: to evaluate the performance gap in these dwellings before and after the renovation and to establish what renovation measures achieve the highest reduction of consumption, particularly in practice (actual savings). The results showed large performance gaps in dwellings with low R and high U values, local heating systems, changes from a non-condensing into a condensing boiler and upgrades to a natural ventilation system. Regarding the actual effectiveness of renovation measures, replacement of old gas boilers with more efficient ones yields the highest energy reduction, followed by deep improvements of windows. Installing mechanical ventilation yields a small reduction compared to other measures, but still much larger than theoretically expected. The paper shows once more that the calculation method currently in use cannot be considered accurate if compared to actual consumption. The study demonstrated that unrealistic theoretical efficiencies of heating systems and insulation values are causing a part of the performance gap. Nowadays, large datasets of buildings thermal performance and actual consumption offer an opportunity to improve these misconceptions.     

A liquefied energy chain for transport and utilization of natural gas for power production with CO2 capture and storage – Part 1

A novel transport chain for stranded natural gas utilized for power production with CO₂ capture and storage is developed. It includes an offshore section, a combined gas carrier, and an onshore integrated receiving terminal. Due to utilization of the cold exergy both in the offshore and onshore processes, and combined use of the gas carrier, the transport chain is both energy and cost effective. In this paper, the liquefied energy chain (LEC) is explained, including novel processes for both the offshore field site and onshore market site. In the offshore section, natural gas (NG) is liquefied to LNG by liquid carbon dioxide (LCO₂) and liquid inert nitrogen (LIN), which are used as cold carriers. The LNG is transported in a combined gas carrier to the receiving terminal where it is used as a cooling agent to liquefy CO₂ and nitrogen. The LCO₂ and LIN are transported offshore using the same combined carrier. Pinch and Exergy Analyses are used to determine the optimal offshore and onshore processes and the best transport conditions. The exergy efficiency for a thermodynamically optimized process is 87% and 71% for the offshore and onshore processes, respectively, yielding a total efficiency of 52%. The offshore process is self-supported with power and can operate with few units of rotating equipment and without flammable refrigerants. The loss of natural gas due to power generation for the energy requirements in the LEC processes is roughly one third of the loss in a conventional transport chain for stranded natural gas with CO₂ sequestration. The LEC has several configurations and can be used for small scale (<0.25 MTPA LNG) to large-scale (>5 MTPA LNG) transport. In the example in this paper, the total costs for the simple LEC including transport of natural gas to a 400 MW_net power plant and return of 85% of the corresponding carbon as CO₂ for a total sailing distance of 24 h are 58.1 EUR/tonne LNG excluding or including the cost of power. The total power requirements are 319 kWh/tonne, hence the energy costs are 31.9 EUR/tonne LNG adding up to 90.0 EUR/tonne LNG. The exergy efficiency for this energy chain including power production and CO₂ capture is 46.4% with a total cost of 20.4 EUR/MWh for the produced electricity. The total emissions (in CO₂ equivalents) in the chain are 1–1.5% of the transported CO₂.     

锅炉余热回收实用性改进

通过分析现有的冷凝锅炉存在的问题,在结构上对其进行改动,采用板式换热器模块化组合,设计出空气预热器、烟气冷凝器与锅炉为一体的余热回收锅炉,使锅炉热效率提高的同时,又具有结构紧凑、不易结垢、耐腐蚀能力强、更加安全、稳定可靠、使用寿命长等优点。     

A liquefied energy chain for transport and utilization of natural gas for power production with CO2 capture and storage – Part 3: The combined carrier and onshore storage

A novel energy and cost effective transport chain for stranded natural gas utilized for power production with CO₂ capture and storage is developed. It includes an offshore section, a combined gas carrier and an integrated receiving terminal. The combined carrier will transport liquid carbon dioxide (LCO₂) and liquid nitrogen (LIN) outbound, where natural gas (NG) is cooled and liquefied to LNG by vaporization of LIN and LCO₂ onboard the carrier. The same carrier is used to transport the LNG onshore, where the NG can be used for power production with CO₂ capture. The combined carrier consists of 10 cylindrical tanks with a diameter of 9.2 m and varying lengths from 14 to 40 m. The total ship volume is 13,000 m³. Assuming 85% capture rate of the CO₂, the maximum ship utilization factor (SUF) is 63.4%. Due to the combined use of the storage tanks, the SUF is decreased with 1.4% points to 62%. The ship is equipped with a bi-directional submerged turret loading for anchoring and loading of NG and unloading of CO₂. Two ships can deliver NG to and remove CO₂ from a 400 MW_net power plant, and still obtain continuous production of LNG offshore without intermediate storage. The investment cost for each gas carrier is 40 million EUR giving total transport cost of 16.9 EUR/tonne LNG. The cost for the offshore transfer system is 6.6 million EUR per tonne LNG, whereas the cost for onshore storage and loading system is 3.1 and 0.8 million EUR per tonne LNG, respectively. The total specific costs for the ship transport, including onshore storage, loading shipping and offshore unloading are 27.5 EUR per tonne LNG for a roundtrip of 5 days, including voyage, production of LNG, unloading, connecting and berthing.     

Coal utilization in industrial boilers in China —a prospect for mitigating CO2 emissions

It is estimated from GEF statistical data for 1991 that more than 500,000 industrial boilers (mostly stoker-fired) in China consume over 400 million tons of coal per year. Each year, because of low boiler efficiency, 75 million tons of coal is wasted and 130 million tons of excess CO₂ are emitted. An analysis of 250 boiler thermal-balance test certificates and 6 field visits in three provinces have shown that: (1) boilers with efficiencies of less than 70% account for 75% of the total boiler-population; (2) the main causes of the low efficiencies are high excess air and unburned carbon in the slag and fly ash. The effect of unburned carbon on CO₂ emission is a balance of positive and negative contributions: while the unburned carbon does not produce CO₂ emissions, its replacement carbon, burned at a low efficiency, contributes to a net increase in CO₂ emissions. It seems from the analysis that the average boiler efficiency can be raised to 73% by relatively simple means, such as the size grading of the coal, improved boiler operating practice and some inexpensive equipment modifications. This could then result in savings each year of 34 million tons of coal and a reduction in CO₂ emissions of 63 million tons at an estimated cost of $10 per ton of CO₂.     

On the potential trade-offs between energy supply and end-use technologies for residential heating

In Sweden, where district heating accounts for a significant share of residential heating, it has been argued that improvements in end-use energy efficiency may be counter-productive since such measures reduce the potential of energy efficient combined heat and power production. In this paper we model how the potential trade-offs between energy supply and end-use technologies depend on climate policy and energy prices. The model optimizes a combination of energy efficiency measures, technologies and fuels for heat supply and district heating extensions over a 50 year period. We ask under what circumstances improved end-use efficiency may be cost-effective in buildings connected to district heating? The answer hinges on the available technologies for electricity production. In a scenario with no alternatives to basic condensing electricity production, high CO₂ prices result in very high electricity prices, high profitability of combined heat and power production, and little incentive to reduce heat demand in buildings with district heating. In contrast, in a scenario where electricity production alternatives with low CO₂ emissions are available, the electricity price will level out at high CO₂ prices. This gives heat prices that increase with the CO₂ price and make end-use efficiency cost-effective also in buildings with district heating.     

The pollutant discharge improvement by introducing HHO gas into biomass boiler

Biomass fuel has been widely concerned because its net CO₂ emission is close to zero. Biomass boilers are known to have lower pollutant emissions than fossil fuel boilers, but in some applications, they also release high-level CO and NO. We developed a medium-sized hydrogen and oxygen (HHO) generator, with high energy conversion rate and adjustable output gas. The HHO gas was then introduced into a biomass hot air generator for mixed combustion. The experimental results showed that based on the electricity consumption of gas production and biomass fuel price, the total cost during preheating reduced. In addition, the average concentrations of CO, NO and smoke decreased by 93.0%, 22.5% and 80%, respectively. Integration of biomass fuel and HHO gas can effectively reduce pollutant emissions and save fuel, especially in areas rich in renewable energy.     

Determinants of the costs of carbon capture and sequestration for expanding electricity generation capacity

This study models the costs of electricity generation with carbon capture and sequestration (CCS), from generation at the power plant to carbon injection at the reservoir, examining the economic factors that affect technology choice and CCS costs at the individual plant level. The results suggest that natural gas and coal prices have profound impacts on the carbon price needed to induce CCS. To extend previous analyses we develop a "cost region" graph that models technology choice as a function of carbon and fuel prices. Generally, the least-cost technology at low carbon prices is pulverized coal, while intermediate carbon prices favor natural gas technologies and high carbon prices favor coal gasification with capture. However, the specific carbon prices at which these transitions occur is largely determined by the price of natural gas. For instance, the CCS-justifying carbon price ranges from $27/t CO₂ at high natural gas prices to $54/t CO₂ at low natural gas prices. This result has important implications for potential climate change legislation. The capital costs of the generation and CO₂ capture plant are also highly important, while pipeline distance and criteria pollutant control are less significant.     

Carbon prices and CCS investment: A comparative study between the European Union and China

Carbon Capture and Storage is considered as a key option for climate change mitigation; policy makers and investors need to know when CCS becomes economically attractive. Integrating CCS in a power plant adds significant costs which can be offset by a sufficient CO₂ price. However, most markets have failed: currently, the weak carbon price threatens CCS deployment in the European Union (EU). In China, a carbon regulation is appearing and CCS encounters a rising interest. This study investigates two questions: how much is the extra-cost of a CCS plant in the EU in comparison with China? Second, what is the CO₂ price beyond which CCS plants become more profitable than reference plants in the EU and in China? To address these issues, I conducted a literature review on public studies about CCS costs. To objectively assess the profitability of CCS plants, I constructed a net present value model to calculate the Levelised Cost of Electricity and the breakeven CO₂ price. CCS plants become the most profitable plant type beyond 115 €/tCO₂ in the EU vs. 45 €/tCO₂ in China (offshore transport and storage costs). I advise on the optimal plant type choice depending on the CO₂ price in both countries.     

An economic assessment of the use of short-rotation coppice woody biomass to heat greenhouses in southern Canada

This study explores the economic feasibility of fossil fuel substitution with biomass from short-rotation willow plantations as an option for greenhouse heating in southern Ontario, Canada. We assess the net displacement value of fossil fuel biomass combustion systems with an integrated purpose-grown biomass production enterprise. Key project parameters include greenhouse size, heating requirements, boiler capital costs and biomass establishment and management costs. Several metrics have been used to examine feasibility including net present value, internal rate of return, payback period, and the minimum or break-even prices for natural gas and heating oil for which the biomass substitution operations become financially attractive. Depending on certain key assumptions, internal rates of return ranged from 11-14% for displacing heating oil to 0-4% for displacing natural gas with woody biomass. The biomass heating projects have payback periods of 10 to >22 years for substituting heating oil and 18 to >22 years for replacing a natural gas. Sensitivity analyses indicate that fossil fuel price and efficiency of the boiler heating system are critical elements in the analyses and research on methods to improve growth and yield and reduce silviculture costs could have a large beneficial impact on the feasibility of this type of bioenergy enterprise.