Anaerobic digestion (AD) is a sustainable waste management technology that primarily generates two products: biogas and digestate. The technology relies on the microorganisms' activity, which depends on several operational factors, such as pH, temperature, solid contents, and ammonia levels. Ammonia is an inorganic form of nitrogen resulting from the biodegradation of organic nitrogen. It is considered one of the major concerns for AD operations due to its inhibitory effects on some microorganisms, particularly methanogens. A common feedstock characterized by high nitrogen content is poultry manure (PM). PM is often avoided in anaerobic digesters due to the anticipated inhibition resulting from its high ammonia levels. However, since poultry manure is one of the most widely available organic wastes, researchers have extensively investigated ways to include PM as a primary feedstock for AD. One possible way to treat high ammonia levels in digestate is ammonia stripping, the physio-chemical separation of ammonia from a solution by introducing a stripping (carrier) gas. There are a few approaches to performing ammonia stripping in AD applications; the most commonly discussed in the literature are pre-hydrolysis and side-stream ammonia stripping. Pre-hydrolysis ammonia stripping is performed on raw feedstock after increasing pH and temperature and is usually not restricted in selecting the gas carrier. On the other hand, side-stream ammonia stripping is when a portion of the digester's working volume is filtered, and the filtrate is sent to a unit where pH and temperature are increased. The carrier gas in these systems is often limited to anaerobic gases such as biogas or steam. The third and most novel approach is post-hydrolysis ammonia stripping, conducted at an intermediate stage between hydrolysis and methanogenesis in a two-stage AD process. This configuration would address the shortcomings of the other two systems. However, there is minimal information on the feasibility and potential of this approach in the literature. This study aims to comprehensively investigate the post-hydrolysis ammonia stripping approach through the following four phases: Phase I) Proof of Concept; Phase II) Optimization; Phase III) Assessment of Alternative Carrier Gases; and Phase IV: Comparison of Different Ammonia Stripping Configurations. Phase I provided the proof of concept under the batch mode and compared the performance of post-hydrolysis ammonia stripping with two-stage AD and co-digestion to improve poultry manure's methane potential as the primary substrate. It was observed that ammonia stripping successfully improved methane potential by up to 150%, whereas improvements due to two-stage AD and co-digestion were limited to 41 and 9%, respectively. Phase II provided more insight into optimizing the ammonia stripping process. Different stripping conditions were tested (pH 7.8 (unadjusted), 9 and 10, temperature 25 (unadjusted), 40 and 55 °C, and flow rate 300 L/L/hour). The results showed that higher pH and temperature lead to higher removal efficiency. However, it was concluded that optimal conditions ultimately depend on the initial and target ammonia levels. Moreover, Analysis of Variance showed that pH and temperature were significant factors affecting the ammonia removal efficiency. In addition, it was observed that higher stripping temperatures (55 °C) enhanced the digestibility of PM and increased its methane potential more than stripping at 40 °C. It was concluded that the optimum stripping conditions were pH 9.5, temperature 40 or 55 °C, and flowrate of 100 L/L/hour to collectively increase ammonia removal while reducing the associated costs and material handling. In Phase III, renewable natural gas (RNG) was evaluated as a stripping medium in batch testing as a potential replacement for biogas and air. Ammonia stripping with RNG yielded promising results comparable to the application of air in terms of ammonia removal and enhancing biogas production from PM (60 and 69% ammonia removal for RNG and air, respectively). In addition, a metagenomic shotgun analysis showed that most biogas production was conducted through hydrogenotrophic methanogens instead of acetoclastic methanogens, which are more susceptible to high ammonia levels. Phase IV assessed the semi-continuous flow two-stage operation of mesophilic AD reactors coupled with different ammonia stripping configurations. Post-hydrolysis ammonia stripping successfully achieved a stable operation of PM mono-digestion at ammonia levels of 1700 and 2400 mg NH₃-N/L in the cases of stripping with air and RNG, respectively. In addition, post-hydrolysis ammonia stripping in semi-continuous flow mode may have promoted acetoclastic methanogens growth since volatile fatty acid concentrations were reduced in the digesters. Phase IV also proved that the performance of post-hydrolysis ammonia stripping is superior over pre-hydrolysis and side-stream ammonia stripping. In the semi-continuous flow reactors, post-hydrolysis ammonia stripping with air achieved on average 831 L biogas/ kg VS at an organic loading rate (OLR) of 2.6 g VS/L/day, whereas side-stream ammonia stripping resulted in average of 700 L biogas/ kg VS at OLR of 1.8 g VS/L/day and higher ammonia stripping requirements. Having said that, the base scenario (no ammonia stripping) was inhibited, indicating that both ammonia stripping configurations were considered successful in alleviating inhibitory effects of ammonia from poultry manure. Phase IV results also proved that air stripping repeatedly outperformed RNG as stripping mediums by having higher ammonia removal efficiencies resulting in higher methane production. However, stripping with RNG is believed to have more practical advantages than air due to avoiding the risk of oxygen infiltration into the reactor. Moreover, renewable natural gas has proven to be an efficient stripping medium that is available on-site. The final stage of Phase IV tested pre-hydrolysis ammonia stripping using air in batch mode and compared it with post-hydrolysis ammonia stripping. Pre-hydrolysis ammonia stripping provided little to no improvement to the methane potential of PM in batch mode and therefore was excluded from the semi-continuous flow experiment. The four phases of this study demonstrated the flexibility and the superiority of post-hydrolysis ammonia stripping over the other pre-hydrolysis and side-stream ammonia stripping. In addition, post-hydrolysis ammonia stripping was proven efficient and feasible for ammonia removal and enabling the mono- or co-digestion of poultry manure. The study also showed that using RNG instead of biogas can significantly reduce the operational costs of the treatment.

Natural gas has grown in popularity as a fuel for power generation gas turbines. However, changes in fuel composition are a topic of concern since fuel variability can have a great impact on the reliability and performance of the burner design. In particular, autoignition of the premixed fuel and air prior to entering the main burner is a potential concern when using exotic fuel blends. To obtain much-needed data in this area, autoignition experiments for a wide range of likely fuel blends containing CH4 mixed with combinations of C2H6, C3H8, C4H10, C5H12, and H2 were performed in a high-pressure shock tube. However, testing every possible fuel blend combination and interaction was not feasible within a reasonable time and cost. Therefore, to predict the surface response over the complete mixture domain, a special experimental design was developed to significantly reduce the amount of 'trials' needed from 243 to only 41 using the Box-Behnkin factorial design methodology. Kinetics modeling was used to obtain numerical results for this matrix of fuel blends, setting the conditions at a temperature of 800 K and pressure of 17 atm. A further and successful attempt was made to reduce the 41-test matrix to a 21-test matrix. This was done using special mixture experimental techniques. The kinetics model was used to compare the smaller matrix to the expected results of the larger one. The new 21-test matrix produced a numerical correlation that agreed well with the results from the 41-test matrix, indicating that the smaller matrix would provide the same statistical information as the larger one with acceptable precision. iii After the experimental matrix was developed using the design of experiments approach, the physical experiments were performed in the shock tube. Long test times were created by "tailoring" the shock tube using a novel driver gas mixture, obtaining test times of 10 millisecond or more, which made experiments at low temperatures possible. Large discrepancies were found between the predicted results by numerical models and the actual experimental results. The main conclusion from the experiments is that the methane-based mixtures in this study enter a regime with a negative temperature coefficient when plotted in Arhennius form. This means that these mixtures are far more likely to ignite under conditions frequently encountered in a premixer, potentially creating hazardous situations. The experimental results were correlated as a function of the different species. It was found that the effect of higher-order hydrocarbon addition to methane is not as profound as seen at higher temperatures (>1100 K). However, the ignition delay time could still be reduced by a factor two or more. It is therefore evident that potential autoignition could occur within the premixer, given the conditions as stated in this study.

Designing products and processes is a fundamental aspect of engineering that significantly impacts society and the world. Chemical process design aims to create more efficient and sustainable production processes that consume fewer resources and emit less pollution. Mathematical models that accurately describe process behavior are necessary to make informed and responsible decisions. However, as processes become more complex, purely symbolic formulations may be inadequate, and simulations using tailored computer code become necessary. The decision‐making process in optimal design requires a procedure for choosing the best option while complying with the system’s constraints, for which task optimization approaches are well suited. This doctoral thesis focuses on black‐box optimization problems that arise when using process simulators in optimal process design tasks and assesses the potential of derivative‐free, metaheuristics, and surrogate‐based optimization approaches. The optimal design of natural gas liquefaction processes is the case study of this research. To overcome numerical issues from black‐box problems, the first work of this doctoral thesis consisted of using the globally convergent Nelder‐Mead simplex method to the optimal process design problem. The second work introduced surrogate models to assist the search towards the global optimum of the black‐box problem and an adaptive sampling scheme comprising the optimization of an acquisition function with metaheuristics. Kriging as surrogate models to the simulation‐optimization problems are computationally cheaper and effective predictors suitable for global search. The third work aims to overcome the limitations of acquisition function optimization and the use of metaheuristics. The proposed comprehensive mathematical notation of the surrogate optimization problem was readily implementable in algebraic modeling language software. The presented framework includes kriging models of the objective and constraint functions, an adaptive sampling procedure, a heuristic for stopping criteria, and a readily solvable surrogate optimization problem with mathematical programming. The success of the surrogate‐based optimization framework relies on the kriging models’ prediction accuracy regarding the underlying, simulation‐based functions. The fourth publication extends the previous work to multi‐objective black‐box optimization problems. It applies the ε constraint method to transform the multi‐objective surrogate optimization problem into a sequence of single‐objective ones. The ε‐constrained surrogate optimization problems are implemented automatically in algebraic modeling language software and solved using a gradient‐based, state‐of‐the‐art solver. The fifth publication is application-driven and focuses on identifying the most suitable mixed‐refrigerant refrigeration technology for natural gas liquefaction in terms of energy consumption and costs. The study investigates five natural gas liquefaction processes using particle swarm optimization and concludes that there are flaws in the expected relationships between process complexity, energy consumption, and total annualized costs. In conclusion, the research conducted in this doctoral thesis demonstrates the importance and capabilities of using optimization to process simulators. The work presented here highlights the potential of surrogate‐based optimization approaches to significantly reduce the computational cost and guide the search in black‐box optimization problems with chemical process simulators embedded. Overall, this doctoral thesis contributes to developing optimization strategies for complex chemical processes that are essential for addressing some of the current most pressing environmental and social challenges. The methods and insights presented in this work can help engineers and scientists design more sustainable and efficient processes, contributing to a better future for all.

Yes / Adsorbents are developing in the various separation industries; these adsorbents can use to sweeten natural gas and remove hydrogen sulfide. Many commercial adsorbents are not regenerable when exposed to hydrogen sulfide because hydrogen sulfide is highly reactive. For removal, the main challenge when using surface adsorbent, is the dissociation adsorption of and non-regenerability of adsorbent. In this study, ultra-stable Y (USY) zeolite, was chosen to adsorb hydrogen sulfide due to its unique physical and chemical properties. To accurately model the adsorption isotherms, experimental adsorption data were measured in high pressure up to 12 bar for hydrogen sulfide and 21 bar for carbon dioxide, methane, and nitrogen as other natural gas components. The experiments were performed at three temperatures of 283, 293 and 303 K. Toth model fitted the experimental data very well, and the capacity of hydrogen sulfide adsorption on USY at the temperature of 283 K and pressure of 12 bar is 4.47 mmol/g that is noticeable. By performing ten cycles of adsorption and regeneration of hydrogen sulfide on USY, the regenerability of the adsorbent was investigated and compared by conducting a similar test on commercial 13X adsorbent. USY is found to be completely regenerable when exposed to hydrogen sulfide. The Isosteric adsorption heat of hydrogen sulfide on the adsorbent is 18.1 kJ/mol, which indicates physical adsorption, and the order of adsorption capacity of tested compounds on USY is H2S > CO2≫CH4 > N2.

Yes / Dual-fuel HCCI engines allow a relatively small quantity of diesel fuel to be used to ignite a variety of fuels such as natural gas or methane in HCCI mode. The gaseous fuel is mixed with the incoming air, and diesel fuel is sprayed into the cylinder by direct injection. Mathematical modelling is used to investigate the effects of parameters such as premixed ratio (fuel ratio) and pilot fuel injection timing on combustion of a dual-fuel HCCI engines. A CFD package is used with AVL FIRE software to simulate dual-fuel HCCI combustion in detail. The results establish a suitable range of premixed ratio and liquid fuel injection timing for low levels of NOx, CO and HC emissions along with a reliable and efficient combustion. Dual-fuel HCCI mode can increase NOx emission with lower premixed ratios in comparison to normal HCCI engines, but it is shown that the NOx emission reduces above a certain level of the premixed ratio. Due to the requirement of homogenous mixing of liquid fuel with air, the liquid fuel injection is earlier than for diesel engines. It is shown that, with careful control of parameters, dual-fuel HCCI engines have lower emissions in comparison with conventional engines.

<p>  </p> <p>A Cummins 6.7L natural gas engine enabled with VVA was installed in a research test cell at Purdue’s Ray Herrick Laboratories for experimental testing. The stock engine which was connected to an AC dynameter was mounted on a movable test bed outfitted with numerous sensors, a charge air cooler, and an external heat exchanger. In the engine control room, a few different systems were set up to run the dyno, collect data from the engine sensors, and monitor the safety apparatuses in the test cell. </p> <p>After the test cell setup was completed, an initial baseline testing was performed to compare the stock engine operation with the baseline engine data given in the Cummins fuel map. The testing was used to verify the engines stock functionality and troubleshoot some additional issues before setting the boundary conditions. Once the boundary conditions were set, a final stock engine testing was performed at rated to check for repeatability and verify stock engine operation following the engine modifications made to accommodate the VVA. </p> <p>Following the baseline testing, the VVA system was assembled on the standalone rig to verify its operation before mounting it on the engine. In order to run the natural gas valve profiles received from Cummins, the VVA controller gains were retuned and the LVDT sensors were calibrated so that the desired closing, opening and lift behaviors were achieved. After verifying the VVA’s functionality, the hardware was mounted on the engine for the VVA experimental testing. </p> <p>The initial VVA testing was focused on understanding the impacts of intake valve modulation on the gas exchange process. Based on previous simulation work, reductions in pumping work leading to better fuel economy is one expected outcome. Experimental testing data related to the engine performance and operation was used to compare each IVC case to the stock IVC timing. These results were also compared to the previous GT-Power work to identify any apparent trends.</p> <p>Future work includes using VVA to further improve efficiency in the part load region, and reduce knock at higher loads. Additionally, the incorporation of a laser based in-cylinder sensing system will help to optimize the capability of VVA.</p>

Advanced technologies for mixed gas detection are discussed. A calorific measurement technique for hydrogen-natural gas mixtures using ultrasonic transducers is examined. Measuring the speed of sound in the gas medium enables an accurate composition testing of mixed gas. At the beginning, different ultrasonic transducers are tested and a suitable one for gas testing is chosen. A jig is designed to conduct the testing with nitrogen/oxygen mixtures in a proof of principle experiment. Another jig is designed and manufactured to test a transit time ultrasonic method for flow rate calculation in order to obtain a full energy flow measurement. A mixed gas leak detection technique based on laser spectroscopy is also studied. A Mid-Wave Infrared (MWIR) laser is implemented to be used as a source in a direct absorption measurement for methane detection. The implemented MWIR laser uses nonlinear optics to generate a MWIR output. A novel intracavity structure using periodically poled lithium niobate as the nonlinear crystal is implemented, and the highest blackbox efficiency for continuous wave difference frequency generation in the MWIR region is reported, to the best of our knowledge. Currently the output power is around 8.1 mW at 3.5 μm with a 1.058% W-1 blackbox efficiency. Watt level MWIR generation is expected using an optimized setup. At last, a second laser source that operates in the long-wave infrared (LWIR) region was also studied. The discussed laser setup for LWIR generation is similar to the MWIR one with different pump and signal wavelengths and an orientation patterned gallium phosphide (OP-GaP) as the nonlinear crystal. Due to the absorption loss of GaP at the pump wavelength, only mW power level is expected out of the intracavity structure. Some alternative approaches for LWIR generation are discussed. / Thesis / Master of Applied Science (MASc)

No description available.

This dissertation consists of three essays. The first essay estimates a demand function for compressed natural gas as a fuel substitute to diesel fuel for firms with hybrid fleets. The data is from the Energy Information Administration, for the years 1989 to 2009, for 47 states. Results show that an increase of $0.10 in the price of diesel fuel will increase compressed natural gas demand by 5.59%. The second essay focuses on regional trade agreements (RTAs). A number of studies have found that RTAs significantly increase members' trade flows. While recent studies have begun to explore the reasons for this, none have examined whether the RTA trade effect varies systematically with the number and type of policy areas covered by the agreement. While the empirical trade literature has shed considerable light on the trade-creating ability of RTAs (Grant and Lambert, 2008), much less is known about why these agreements are so successful. In this study, we draw on a new database from the World Trade Organization of trade policy areas covered by RTAs to examine whether the degree of trade liberalization is an important determinant of the RTA trade effect. An augmented, theoretically consistent gravity equation is developed to explore the effects of RTAs on trade, conditional on the policy areas they include. In particular, we investigate two policy areas that are particularly important for agricultural trade, sanitary and phytosanitary measures (SPS) and technical barriers to trade (TBT). The results suggest that harmonization of non-tariff measures inside RTAs matters: Agreements that liberalize these policies increase members' agricultural trade by an additional 62 percent compared to agreements that do not. We conclude that studying the components of RTAs -- in particular, the policy areas covered by these agreements -- is important when analyzing the determinants of RTA trade effects. The third essay uses Bayesian Model Averaging (BMA) to study the effect of membership in the General Agreement on Tariffs and Trade (GATT), the predecessor to the World Trade Organization (WTO), and the WTO on trade flows. Existing GATT/WTO literature is not univocal as to whether membership in the GATT/WTO increases trade flows. In this study, Bayesian model averaging (BMA) is used in the presence of theoretical uncertainty to address whether membership in the GATT/WTO plays a role in the gravity model. Several datasets are examined: a dataset from a previous study; and two datasets compiled for this study, world trade and agricultural trade. Results show, for all three sets of data, that membership in the GATT/WTO does belong in the gravity equation and increases trade flows. / Ph. D.

The objective of this thesis is to investigate and compare the performance and emissions characteristics of diesel-ignited methane and diesel-ignited propane dual fuel LTC in a single cylinder research engine (SCRE) at a constant engine load of 5.1 bar net indicated mean effective pressure (IMEP) and at a constant engine speed of 1500 RPM. Percentage of energy substitution of propane or methane (0 - 90 percent), diesel injection timing (SOI: 355 CAD – 280 CAD), rail pressure (200 bar – 1300 bar) and boost pressure (1.1 bar – 1.8 bar) were varied to quantify their impact on engine performance and engine-out ISNOx, ISHC, ISCO, and smoke emissions. Advancing SOI to 310 CAD and beyond yielded simultaneous ISNOx and smoke emissions. A rail pressure of 500 bar was the optimal one for both fueling combinations while increasing boost pressure over 1.2 bar had a very little effect on ISNOx and smoke emissions.