Operational simulation and an economical modelling study on utilizing waste heat energy in a desalination plant and an absorption chiller

PhD ThesisIt is well established that a large proportion of the global emission of greenhouse gases are produced by electricity power stations and that a power plant typically emits about two thirds of its input energy as waste heat into the atmosphere. As such there is a lot of potential for additional applications that utilize this waste heat energy. Utilizing this waste heat energy in a desalination plant to produce low-cost potable water is the key to overcoming three problems at once, namely the water shortage in and and semi-arid areas, the continuing increase in oil prices by being more efficient and global warming. In all waste heat recovery or alternative energy systems based on natural phenomena (solar or wind) a major difficulty is decoupling supply from demand as thermal storage is neither efficient nor practical in many cases. A significant difficulty of gas turbine based power generation systems is the derating caused by high ambient temperatures; typically a 1% change in ambient temperature produces a similar reduction in efficiency. Therefore, by also utilizing this waste heat energy in an absorption chiller to pre-cool the gas turbine's compressor inlet-air, the effect of ambient temperature fluctuations on the gas turbine's performance would be eliminated. The combined cycle described in this study was designed in an attempt to address these issues. A gas turbine based combined heat and power plant was combined further with an absorption refrigeration unit and an MED desalination plant. The absorption unit stabilizes the operation of the gas turbine, reducing the sensitivity to changes in ambient temperature and the desalination plant acts as an energy utilization device that produces a usable product (40,000m3/day of potable water) that is easily stored and distributed as required. The simulation was performed using IPSEpro on the basis of real data obtained from an existing power plant and commercially available plants. The performance of the sub-plants was investigated using energy and exergy analyses, in design and off-design conditions using real weather data obtained from the Presidency of Meteorology and Environment in Saudi Arabia. Two different desalination technologies and two different coupling techniques were examined in four proposed plants. An optimal plant design was chosen from a comparison between all proposed plants' energy and exergy analysis results. The chosen plant was then optimized and simulated in design and off-design conditions. The initial results indicated that the simulated combined power plant's carbon footprint was reduced by 36.8% and its energy utilization factor was improved by 30.97%. This approach also stabilized the effect of ambient temperature fluctuations on the gas turbine's performance. After optimization, the carbon footprint was further reduced by 31.17% and the energy utilization factor was further improved by 6.11%. The energy destroyed through the exhaust stack was reduced by 78% and the proposed plant's overall exergetic efficiency was improved to 49.64%. Furthermore, the desalination plant's concentration factor was reduced by 0.45 and an additional product of a hot water stream at a temperature of 75°C was gained. An economic study was performed that indicated that the optimized plant is economically viable. As part of this analysis, a number of sensitivity studies defined the minimum selling prices of the plant's products and indicated the influence of fuel price, interest rates, capacity factors and project lifetime on the viability of the plant. The results also indicated that the proposed plant is a good investment, offering competitive energy and potable water prices, in regard to the location indicated by this study

Operational simulation and an economical modelling study on utilizing waste heat energy in a desalination plant and an absorption chiller

It is well established that a large proportion of the global emission of greenhouse gases are produced by electricity power stations and that a power plant typically emits about two thirds of its input energy as waste heat into the atmosphere. As such there is a lot of potential for additional applications that utilize this waste heat energy. Utilizing this waste heat energy in a desalination plant to produce low-cost potable water is the key to overcoming three problems at once, namely the water shortage in and and semi-arid areas, the continuing increase in oil prices by being more efficient and global warming. In all waste heat recovery or alternative energy systems based on natural phenomena (solar or wind) a major difficulty is decoupling supply from demand as thermal storage is neither efficient nor practical in many cases. A significant difficulty of gas turbine based power generation systems is the derating caused by high ambient temperatures; typically a 1% change in ambient temperature produces a similar reduction in efficiency. Therefore, by also utilizing this waste heat energy in an absorption chiller to pre-cool the gas turbine's compressor inlet-air, the effect of ambient temperature fluctuations on the gas turbine's performance would be eliminated. The combined cycle described in this study was designed in an attempt to address these issues. A gas turbine based combined heat and power plant was combined further with an absorption refrigeration unit and an MED desalination plant. The absorption unit stabilizes the operation of the gas turbine, reducing the sensitivity to changes in ambient temperature and the desalination plant acts as an energy utilization device that produces a usable product (40,000m3/day of potable water) that is easily stored and distributed as required. The simulation was performed using IPSEpro on the basis of real data obtained from an existing power plant and commercially available plants. The performance of the sub-plants was investigated using energy and exergy analyses, in design and off-design conditions using real weather data obtained from the Presidency of Meteorology and Environment in Saudi Arabia. Two different desalination technologies and two different coupling techniques were examined in four proposed plants. An optimal plant design was chosen from a comparison between all proposed plants' energy and exergy analysis results. The chosen plant was then optimized and simulated in design and off-design conditions. The initial results indicated that the simulated combined power plant's carbon footprint was reduced by 36.8% and its energy utilization factor was improved by 30.97%. This approach also stabilized the effect of ambient temperature fluctuations on the gas turbine's performance. After optimization, the carbon footprint was further reduced by 31.17% and the energy utilization factor was further improved by 6.11%. The energy destroyed through the exhaust stack was reduced by 78% and the proposed plant's overall exergetic efficiency was improved to 49.64%. Furthermore, the desalination plant's concentration factor was reduced by 0.45 and an additional product of a hot water stream at a temperature of 75°C was gained. An economic study was performed that indicated that the optimized plant is economically viable. As part of this analysis, a number of sensitivity studies defined the minimum selling prices of the plant's products and indicated the influence of fuel price, interest rates, capacity factors and project lifetime on the viability of the plant. The results also indicated that the proposed plant is a good investment, offering competitive energy and potable water prices, in regard to the location indicated by this study.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The Prevalence of Headache and Associated Factors in Al-Kharj, Saudi Arabia: A Cross-Sectional Study

Background. Only few studies have investigated the prevalence and risk factors of headaches among the Saudi population. The study aimed to estimate the prevalence of headache and to explore its associated risk factors Al-Kharj, Saudi Arabia. Methods. The multistage sampling technique was used to enroll 1200 population-based participants who were asked to complete a self-administered questionnaire about headaches, demographics, and several other parameters such as smoking status and different chronic and psychological illnesses. The chi-square test and multivariate logistic regression analysis were used to test the association. Results. The overall prevalence of headaches in this study was 3%. The multiple logistic regression analysis showed that females were more likely to have headaches than males (odds ratio (OR) 0.735, 95% confidence interval (CI) = 0.612–1.341; P=0.024). Being a current smoker was also significantly associated with higher “odds” of having headache (OR = 1.319, 95% CI = 0.932–2.462; P=0.037). Participants who were overweight had a significantly higher risk of headache (OR = 1.631, 95% CI = 1.48–1.854; P=0.037). Nonmarried people were significantly more likely to have headache pain, compared to married individuals (OR = 0.875, 95% CI = 0.646–2.317; P=0.047). Conclusion. The prevalence of headaches was 3%, and four significant associated factors were identified: females, nonmarried, smoking, and overweight. The temporality of the relationship between these factors and headache cannot be confirmed in this cross-sectional study; so future longitudinal studies are needed to confirm these potential causal relationships

SARS-CoV-2 vaccination modelling for safe surgery to save lives: data from an international prospective cohort study

Background: Preoperative SARS-CoV-2 vaccination could support safer elective surgery. Vaccine numbers are limited so this study aimed to inform their prioritization by modelling. Methods: The primary outcome was the number needed to vaccinate (NNV) to prevent one COVID-19-related death in 1 year. NNVs were based on postoperative SARS-CoV-2 rates and mortality in an international cohort study (surgical patients), and community SARS-CoV-2 incidence and case fatality data (general population). NNV estimates were stratified by age (18-49, 50-69, 70 or more years) and type of surgery. Best- and worst-case scenarios were used to describe uncertainty. Results: NNVs were more favourable in surgical patients than the general population. The most favourable NNVs were in patients aged 70 years or more needing cancer surgery (351; best case 196, worst case 816) or non-cancer surgery (733; best case 407, worst case 1664). Both exceeded the NNV in the general population (1840; best case 1196, worst case 3066). NNVs for surgical patients remained favourable at a range of SARS-CoV-2 incidence rates in sensitivity analysis modelling. Globally, prioritizing preoperative vaccination of patients needing elective surgery ahead of the general population could prevent an additional 58 687 (best case 115 007, worst case 20 177) COVID-19-related deaths in 1 year. Conclusion: As global roll out of SARS-CoV-2 vaccination proceeds, patients needing elective surgery should be prioritized ahead of the general population