Modelling three-phase releases of carbon dioxide from high-pressure pipelines

This paper describes the development and experimental validation of a three-phase flow model for predicting the transient outflow following the failure of pressurised CO₂ pipelines and vessels. The choked flow parameters at the rupture plane, spanning the dense-phase and saturated conditions to below the triple point, are modelled by maximisation of the mass flowrate with respect to pressure and solids mass fraction at the triple point. The pertinent solid/vapour/liquid phase equilibrium data are predicted using an extended Peng–Robinson equation of state.The proposed outflow model is successfully validated against experimental data obtained from high-pressure CO₂ releases performed as part of the FP7 CO2PipeHaz project (www.co2pipehaz.eu).The formation of solid phase CO₂ at the triple point is marked by a stabilisation in pressure as confirmed by both theory and experimental observation. For a fixed diameter hypothetical pipeline at 100 bar and 20 °C, the flow model is used to determine the impact of the pipeline length on the time taken to commence solid CO₂ discharge following its rupture.     

An Experimental Study on Pyrolysis of Biomass

In this study, pyrolysis of sugarcane bagasse was performed in fixed bed tubular reactor under the conditions of nitrogen atmosphere, by varying temperature and different particle sizes. The effect of final pyrolysis temperature from 400 to 500°C and the nitrogen flow rate from 50 to 200 cc min⁻¹ on the pyrolysis product yields from sugarcane bagasse have been investigated. The Maximum bio-oil yield obtained is 24.12 wt% at the final pyrolysis temperature of 450°C, N₂ flow rate of 50 cc min⁻¹ and particle size of mesh number −8 + 12. The yield of bio-oil decreases with increase in temperature from 450 to 550°C and N₂ flow rate from 50 to 200 cc min⁻¹. The various characteristics of pyrolysis oil obtained under these conditions were identified on the basis of standard test methods. The empirical formula of pyrolysis oil with a heating value of 37.01 MJ Kg⁻¹ was established as CH_1.434 O_0.555 N_0.004. The results from the pyrolysis show the potential of sugarcane bagasse as an important source of liquid hydrocarbon fuel.     

Partial nitritation of landfill leachate with varying influent composition under intermittent aeration conditions

The start-up and operation of a partial nitritation sequencing batch reactor for the treatment of landfill leachate were carried out on intermittent aeration mode. Partial nitrite accumulation was established in 15 days after the mode was changed from continuous aeration to intermittent aeration. Despite the varying influent composition, partial nitritation could be maintained by adjusting the hydraulic retention time (HRT) and the air flow rate. An increase in the air flow rate together with a decrease in air off duration can improve the partial nitritation capacity and eventually result in the development of granular sludge with fine diameters. A nitrogen loading rate of 0.71 ± 0.14 kg/m³/d and a COD removal rate of 2.21 ± 0.13 kg/m³/d were achieved under the conditions of an air flow rate of 19.36 ± 1.71 m³ air/m³/h and an air on/off duration of 1.5 min/0.7 min. When the ratio of total air flux (TAF) to the influent loading rate (ILR) was controlled at the range of 163–256 m³ air/kg COD, a stable effluent NO₃^?–N/NO_x^?–N (NO₂^?–N plus NO₃^?–N) ratio below 13% was achieved. Interestingly, the effluent pH was found to be a good indicator of the effluent NO₂^?–N/NH₄⁺–N ratio, which is an essential parameter for a subsequent anaerobic ammonium oxidation (Anammox) reactor.     

Disintegration of waste activated sludge by different applications of Fenton process

Oxidative disintegration of municipal waste activated sludge (WAS) using conventional Fenton (Fe²⁺ + H₂O₂, CFP) and Fenton type (Fe⁰ + H₂O₂, FTP) processes was investigated and compared in terms of the efficiency of sludge disintegration and enhancement of anaerobic biodegradability. The influences of different operational variables namely sludge pH, initial concentration of Fe²⁺ or Fe⁰, and H₂O₂ were studied in detail. The optimum conditions have been found as catalyst iron dosage = 4 g/kg TS, H₂O₂ dosage = 40 g/kg TS and pH = 3 within 1 h oxidation period for both CFP and FTP. Kinetics studies were performed under optimal conditions. It was determined that the sludge disintegration was happened in two stages by both processes: rapid and subsequent slow disintegration stages and rapid sludge disintegration stage can be described by a zero-order kinetic model. The effects of oxidative sludge disintegration under the optimum conditions on anaerobic digestion were experienced with biochemical methane potential (BMP) assay in batch anaerobic reactors. Total methane production in the CFP and FTP pre-treated reactors increased by 26.9% and 38.0%, relative to the untreated reactor (digested the raw WAS). Furthermore, the total chemical oxygen demand reductions in the pre-treated reactors were improved as well.     

Environmental and eco-costs life cycle assessment of an acrylonitrile process by capacity enlargement in Mexico

Life cycle assessment and marginal prevention costs (eco-costs method) for an acrylonitrile plant were carried out estimating the environmental impact and the eco-costs, due to the increment in the production capacity. This study compares the old plant's operative performance (old design) at 50,000 ton/year where the by-products were incinerated, with the current operation at 60,000 ton/year where those by-products in the waste stream will be treated to take advantage of its substance content, to generate profitable products. In addition, the effect of a wastewater flow rate with cyanide was evaluated on the biological wastewater treatment process.The redesign showed a high reduction percentage in eleven of eighteen midpoint impact categories. The reduction of 36% in the global impacts in the redesign was obtained when these ones were calculated based on the impacts of the year of 2005. The CO₂ emissions equivalents (CO₂eq) had a reduction of 46% (from 6.55 to 3.50 kg CO₂eq/kg of acrylonitrile). The total of marginal prevention costs (eco-costs) are 1.28 USD/kg for acrylonitrile old design and the 0.735 USD/kg for acrylonitrile redesign, i.e. 42.5% lower than the old design. This means that 94.5% are costs for pollution and the use of energy and 5.4% by depletions of material resources.This study proved that the redesign is environmentally most favorable and economically affordable method.Eco-costs method should be incorporated as part of the financial indicators of a project, but with the respective adaptation to the environmental and economic conditions of a region.     

pH-conditioning for simultaneous removal of arsenic and iron ions from groundwater

The effects of some commonly used pH conditioners, viz., lime, banana ash, the carbonate and the bicarbonate of sodium and potassium and their binary mixture, on simultaneous removal of arsenic and iron ions from water have been studied. KHCO₃ has been found to be the most suitable pH conditioner for the purpose. About 80 mg/L KHCO₃ can remove both arsenate and iron ions from initial 250 μg/L and 20 mg/L to below their respective guideline values of the WHO for drinking water, retaining the final pH in the acceptable range for drinking. The simultaneous removal of arsenate and iron by the pH-conditioners decreases in the order: Lime > KHCO₃ > NaHCO₃ > K₂CO₃ > Na₂CO₃ > ash. However, lime requires post-treatment correction of highly alkaline pH. The arsenate ion is removed predominantly through goethite or ferrihydrite in the presence of the bicarbonates and through ferric hydroxide in the presence of the more alkaline pH-conditioners. KHCO₃ is more advantageous over the more basic substances including NaHCO₃, because with it, one not only needs the smallest dose but also can avoid careful adjustment of the dose for regulating the initial and the final pH. The paper clearly demonstrates the potential of KHCO₃ to substitute the currently used pH-conditioners, viz., ash, lime and NaHCO₃ for simultaneous removal of arsenate and iron ions.     

Corrosion behavior of steels for CO2 injection

The process chain for Carbon Capture and Sequestration (CCS) includes tubing for injection of CO₂ into saline aquifers. The compressed CO₂ is likely to contain specific impurities; small concentrations of SO₂ and NO₂ in combination with oxygen and humidity are most harmful. In addition, CO₂ saturated brine is supposed to rise in the well when the injection process is interrupted. The material selection has to ensure that neither CO₂ nor brine or a combination of both will leak out of the inner tubing. In this comprehensive paper the investigated materials range from low-alloy steels and 13% Cr steels up to high-alloy materials. Electrochemical tests as well as long term exposure tests were performed in CO₂, in brine and combination of both; pressure was up to 100 bar, temperature up to 60 °C. Whereas the CO₂ stream itself can be handled using low alloy steels, combinations of CO₂ and brine require more resistant materials to control the strong tendency to pitting corrosion. The corrosion behavior of heat-treated steels depends on factors such as microstructure and carbon content. For different sections of the injection tube, appropriate materials should be used to guarantee safety and consider cost effectiveness.     

On–off control of aeration time in the simultaneous removal of ammonia and manganese using a biological aerated filter system

The biological aerated filter (BAF) system, a new alternative in drinking water treatment, was designed to remove NH₄⁺–N and Mn²⁺ simultaneously. This study aimed to control the aeration time in the BAF system for simultaneous NH₄⁺–N and Mn²⁺ removal to achieve the Malaysian effluent quality regulation for drinking water. The experiment was conducted under four strategies of S1, S2, S3 and S4. The results demonstrated that acceptable levels of NH₄⁺–N and Mn²⁺ were achieved over a 6 h aeration period (S1), producing effluent concentrations of 0.7 mg/L (93.2% removal) and 0.08 mg/L (79.6% removal), respectively. At the initial treatment of S1 and S2, the dissolved oxygen (DO) level rapidly increased until it reached a saturated concentration (6.8 mg/L DO) after 2 h period. Automatic on–off aeration time to maintain 3 mg/L DO set point (S4) resulted with a good effluent quality of NH₄⁺–N and Mn²⁺ compared with the 2 mg/L DO set point (S3) which did not meet the regulated standard limits. Through the automatic on–off aeration time, the saturated and excessive DO levels in the BAF system can be avoided consequently reduce the wastage of energy and electrical consumption for simultaneous NH₄⁺–N and Mn²⁺ removal from drinking water treatment.     

Explosions and deflagration-to-detonation transitions in epoxy propane/air mixtures

The explosion and deflagration-to-detonation transition (DDT) in epoxy propane (E.P.) vapor/air mixture clouds under weak ignition conditions has been studied in an experimental tube of diameter 199 mm and length 29.6 m. E.P. vapor clouds were formed by injecting liquid E.P. into the experimental tube and evaporating of the fine E.P. droplets. The dimension and the evaporating process of the E.P. droplet were measured and analyzed. The E.P. vapor/air mixture clouds were ignited by an electric spark with an ignition energy of 40 J. The characteristics and the stages of the DDT process in the E.P. vapor/air mixtures have been studied and analyzed. A self-sustained detonation wave formed, as was evident from the existence of a transverse wave and a cellular structure. Moreover, a retonation wave formed during the DDT process in the E.P. vapor/air mixture. The influence of the E.P. vapor concentration on the DDT process has been studied. The minimum E.P. vapor concentration for the occurrence of the DDT in the E.P. vapor/air mixture has been evaluated and the variation of DDT distance with E.P. vapor concentration has been analyzed.     

Optimization and evaluation of an air-recirculated stripping for ammonia removal from the anaerobic digestate of pig manure

An air-recirculated stripping involved two processes and did not require any pretreatment. First, stripping CO₂ decreased the buffer capacity of the anaerobic digestate, thereby reducing the amount of lime used to achieve a high pH. Second, lime was added to increase pH and remove ammonia from the anaerobic digestate of pig manure. pH increased from 8.03 to 8.86 by stripping CO₂ in the first process (gas-to-liquid ratio = 180) and further reached 12.38 in the second process (gas-to-liquid ratio = 300). During process optimization, the maximum ammonia removal efficiency reached 96.78% with a lime dose of 22.13 g. The value was close to 98.25%, which was the optimal result predicted by response surface methodology using the software Design-Expert 8.05b. All these results indicated that air-recirculated stripping coupled with absorption was a promising technology for the removal and recovery of nitrogen in the anaerobic digestate of pig manure.     

Achieving stable partial nitritation using endpoint pH control in an SBR treating landfill leachate

The feasibility of using endpoint pH control to achieve stable partial nitritation (PN) in an SBR for landfill leachate treatment was investigated. By imposing a fixed-time anoxia followed by variable-time aeration in an SBR cycle, successful partial nitritation was maintained for 182 days at a nitrogen loading rate of 0.30–0.89 kg/m³/day. The effluent NO₂⁻-N/NH₄⁺-N ratio and the effluent NO₃⁻-N concentration were 1.30 ± 0.22 and 16 ± 9 mg/L, respectively. High free ammonia (FA) and low dissolved oxygen (DO) concentrations were inhibition factors of nitrate formation. The termination of aeration at a suitable endpoint pH was the key to achieve an effluent NO₂⁻-N/NH₄⁺-N ratio close to the stoichiometric value. This endpoint pH control strategy represents practical potentials in the engineered application of combined PN–ANAMMOX processes.     

Removal of H2S by co-immobilized bacteria and fungi biocatalysts in a bio-trickling filter

Biological control of odor gases has gained more attention in recent years. In this study, removal performance of a vertical bio-trickling filter inoculated with bacteria and fungi was studied. Bacteria and fungi were isolated from activated sludge in a sewage treatment plant. By adopting “three step immobilization method”, the bio-trickling filter could degrade pollutant immediately once hydrogen sulfide (H₂S) passed. The optimal empty bed resident time was 20 s. The optimal elimination capacity was about 60 g H₂S m^?3 h^?1 with removal efficiency of 95%. And the maximum elimination capacity was 170 g H₂S m^?3 h^?1. Pressure drop was ranged between 5 and 15 mm H₂O per bed over the whole operation. Removal efficiency was not affected obviously after terminating nutrient supply. The bio-trickling filter could recover back after shut down H₂S gaseous and liquid supplies simultaneously. Microbial community structure in the bio-trickling filter was not changed significantly.Combining bacteria and fungi would be a better choice for inoculation into a bio-trickling filter because of the quickly degradation of H₂S and rapid recovery under shut-down experiment. This is the first study attempting to combine bacteria and fungi for removal of H₂S in a bio-trickling filter.     

Flammability of hydrocarbon and carbon dioxide mixtures

The effect of carbon dioxide (CO₂) concentration on the ignition behaviour of hydrocarbon and CO₂ gas mixtures is examined in both jets and confined explosions. Results from explosion tests are presented using a 20 l explosion sphere and an 8 m long section of 1.04 m diameter pipeline. Experiments to assess the flame stability and ignition probability in free-jets are reported for a range of different release velocities. An empirically-based flammability factor model for free-jets is also presented and results are compared to ignition probability measurements previously reported in the literature and those resulting from the present tests.The results help to understand how CO₂ changes the severity of fires and explosions resulting from hydrocarbon releases. They also demonstrate that it is possible to ignite gas mixtures when the mean concentration is outside the flammable range. This information may be useful for risk assessments of offshore platforms involved in carbon sequestration or enhanced oil recovery, or in assessing the hazards posed by poorly-inerted hydrocarbon processing plant.     

Experimental simulation of airbag deployment for pipeline closing

Small scale tests were carried out at ISL's shock tube facility STA (100 mm inner diameter) to study the problem of closing a pipeline by means of an airbag in case of explosions or gas leakages. Experiments were carried out to simulate the flow in a pipeline at velocities and gas pressures as present in pipeline flows. In this study the gas used was nitrogen at static pressures of 0.2 up to 5 MPa and at flow velocities of 25 m/s up to 170 m/s. A special Nylon airbag, deployed from the tube wall into the pipe, was used to simulate the airbag inflation in a real pipeline. For this purpose a special gas filling system consisting of a gas generator with a reservoir volume of up to 500 cm³ which permits air pressures up to 17 MPa to be generated inside the airbag was developed at ISL. With a fast pyrotechnically opened valve the reservoir gas was released for airbag filling. The airbag inflation was triggered in such a way that it opened in nearly 3 ms into the pipe flow generated by the shock tube and continued for about 10 ms. For this application a special measuring chamber was designed and constructed with 20 measuring ports. Through two window ports, located one in front of the other, the airbag inflation could be visualized with up to 50 successive flash sparks illuminating a fast rotating film inside a drum camera. Pressure measurements using commercially available PCB pressure gauges at 9 measuring ports placed along the inner tube surface gave some hints on the behaviour of the wall pressure during airbag deployment. As a result from the experiments performed it is to conclude, that, with the Nylon airbag samples available, the pipe flow cannot be blocked by the inflating airbag. The flow forces acting on the airbag during deployment are in the shock tube experiments of the order of about 1000 N, which are not balanced by the airbags' neck, fixing it to the shock tube wall. This outcome suggests that a mechanical support is required to fix the airbag in its place during inflation.     

Calorimetric behaviors of N2H4 by DSC and superCRC

The objective of this study is to obtain information about the thermal decomposition behaviors of hydrazine (N₂H₄) caused by metals, using differential scanning calorimeter (DSC) and SuperCRC. The DSC measurements revealed that the exothermic reactions of N₂H₄ were caused by the reaction conditions such as the type of cells; the T_DSC with a gold pan is 485.2 K and that with a glass capillary is 620.5 K. Besides, the activation energy of the thermal decomposition of N₂H₄, calculated from the Kissinger and Ozawa methods, were found to be about 38±2 kJ mol⁻¹ in the gold pan and 141±8 kJ mol⁻¹ in the glass capillary. Moreover, a heat flow profile was observed with SuperCRC during the mixing of N₂H₄ and the metal ion solution at 298 K. The maximum heat flow was related to the metal ion oxidative characters. The higher oxidative characters would provide a faster acceleration for the exothermic behavior than the lower oxidative ions. Based on this study, Mn(VII) and Cr(VI) were considered to exhibit strongly oxidative characteristics during mixing with N₂H₄.     

Enhanced NOx removal from flue gas by an integrated process of chemical absorption coupled with two-stage biological reduction using immobilized microorganisms

An integrated process of metal chelate absorption coupled with two stage bio-reduction using immobilized cultures has been proposed to continuously removal of NO_x, and the effects of SO₂, NO and O₂ concentration, gas/liquid flow rate on NO_x removal efficiency were investigated. Although nitrogen-containing components, such as Fe(II)EDTA-NO, NO₂^? and NO₃^? in the scrubbing solution, inhibited the bio-reduction of Fe(III)EDTA obviously, it was feasible to abate the inhibition effect by using the two stage bio-reduction system, and thus to improve NO_x removal efficiency. The removal efficiency decreased slowly with the increase of SO₂, O₂, NO concentration and gas flow rate, and increased with the increase of liquid flow rate. Continuously operating for 18 days, a high removal efficiency around 95% was reached by using the two-stage bio-reduction system with immobilized microorganisms, while the value decreased to 85% after 5 days of operation by using the suspended microorganisms, at a constant gas flow rate of 60 L/h containing 424–450 mg/m³ NO, 2428–2532 mg/m³ SO₂ and 3% O₂.     

Removal of VOCs emitted from p-xylene liquid storage tanks by a full-scale compost biofilter

A full-scale compost biofilter system (CBS) was built to treat vapor losses emitted from three analogous vertical fixed roof p-xylene (p-X) liquid storage tanks of 7500 m³ total working volume. The CBS showed a stable and efficient treatment of standing loss (L_S) and working loss (L_W) with an average removal efficiency of 95.4% through 18-month standing storage and filling operation of the tanks. The weight of activated carbon employed in the concentration buffer influences the CBS performance for L_W treatment under high organic loads. The daily average pressure drops across biofilter bed displayed very low with a maximum of 7.6 mm-H₂O. This reflects that the CBS can be operated without stress and compression of biofilter bed and thus reduce maintenance frequency. No additional inputs of chemicals and fuels along with low electricity and water usage helped in its prolonged operation and increased its cost effectiveness. These advantages make the CSB become a promising control technology of vapor losses emitted from fixed roof organic liquid storage tanks.     

Optimization of Innovative Ethanol Production from Wheat by Response Surface Methodology

A soft wheat variety has been tested as the raw material for fuel ethanol production via a novel processing route. The bran stream produced by the break section of a Buhler mill was used as the sole nutrient source in solid-state fermentation for the production of hydrolytic enzymes by two fungal strains, Aspergillus awamori and Aspergillus oryzae. Co-fermentation of the two fungi was largely problematic because of a significant difference between their growth rates. A mixture of the two enzyme solutions produced by separate cultivation of the two strains was effective for simultaneous starch and protein hydrolyses. Response surface methodology was used to design ethanol production trials using the flour hydrolysate as the only nutrient source by Saccharomyces cerevisiae. In a medium containing 150 g l⁻¹ glucose and 310 mg l⁻¹ free amino nitrogen, ethanol yield on glucose reached 50.7%, i.e., 99.2% of the theoretical conversion ratio, in 72 h. The yield of CO₂ from glucose was approximated as slightly higher than its theoretical yield due possibly to the availability of O₂ in the early fermentation stage. The overall production of 2-methyl-1-butanol, 1-propanol, 2-methyl-1-propanol and 3-methyl-butanol in all trials of yeast fermentation remained below 1000 ppm. Mass balance calculation concluded conversion ratios of 29.61% (w/w) ethanol and 23.74% (w/w) CO₂ from the wheat.     

Optimizing the preparation parameters of mesoporous nanocrystalline titania and its photocatalytic activity in water: Physical properties and growth mechanisms

Titania nanomaterial with an anatase structure and 5.6 nm crystallite size and 280.7 m² g⁻¹ specific surface areas had been successfully prepared by sol–gel/hydrothermal route. The effect of pH as a type of autoclave and calcination was studied. Crystallite size and phase composition of the prepared samples were identified. X-ray diffraction analyses showed the presence of anatase with little or no rutile phases. The crystallite size of the prepared TiO₂ with acidic catalyst was both smaller than that prepared with basic catalyst, and was increasing after acidic calcinations by a factor 4–5. Basic calcinations produced a specific increase of 1.5. Rutile ratio and the particle size were increased after calcination at 500 °C. However, TiO₂ powder synthesized using a basic catalyst persisted the anatase phase and a loosely aggregation of particles. Anatase TiO₂ as prepared with acidic catalyst in Teflon lined stainless steel autoclave demonstrated the highest photocatalytic activity for degradation of 2,6-dichlorophenol-indophenol under ultraviolet irradiation with t_½ 0.8 min.