While much research has been published on the Compost Heat Recovery Systems (CHRs), little has been documented on the design and performance evaluation of the Hydronic compost heat exchangers using ...numerical and computational methods, occasionally resulting in compost process inhibition. A CHRs (0.036 m
3
/7.2 m
2
) Hydronic-type heat exchanger and 12.43 m
2
/2.83 m
3
, compost reactor (CR), was designed and developed with the main objective of evaluating the design and its performance. The numerical design and performance evaluation was achieved by using Kern's and the effectiveness and Number of Transfer Units methods (ε-NTU), respectively. Empirically, data were captured by using the Polytetrafluoroethylene (PTFE) thermocouples connected to the TC-8 Picolog Data loggers. Data validation (empirical and mathematical), was achieved by modifying a free computer-based software developed by the Chemical Engineering Calculations (CHECAL), into a Hydronic Compost Heat Exchanger design and performance evaluation software (HYDROCOHE). Between the HYDROCOHE and numerical, and between empirical and HYDROCOHE, R
2
values of 0.99938-0.9995, and R
2
of 0.99269-0.9432 with the effectiveness of 0.4853-0.4848 were achieved with 0.99 kW-empirical and 2.10 kW-HYDROCOHE, respectively. The power disparity may be ascribed to the compost reactor's insufficient thermal insulation. Counterflow arrangement was more effective (0.4766) than crossflow (0.4622) and parallelflow (0.4430) setups. Parallelflow heat exchanger system, therefore, has the potential to extract heat steadily, minimizing the composting cycle inhibition. Further work on the impact of various flowrates on the direction of flow and heat extraction is recommended.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Sustainability science still struggles with transitioning from problem-focused to solution-oriented endeavors that yield positive impacts on mitigating sustainability challenges. This article ...presents and compares three sustainability science studies on the reconstruction after the 2011 triple-disaster in Japan; limited energy and livelihood options in rural Africa; and toxic chemical dispersion in San Francisco. Research varied in design and conduct, with opportunities for improvement in transdisciplinary collaboration, institutional incentives and rewards, competency development in future researchers, articulation of relevant political economies, and orientation towards feasible solution options. Of particular interest are insights synthesized across the cases, mainly success factors and their transferability, sustainability science pedagogical opportunities, and potential future research areas. These insights emerged from presentations and breakout discussions of the three studies at the 2012 International Conference on Sustainability Science held at Arizona State University.
The generation of power within Southern Africa is reviewed. A study is described in which the emission factors for CO2 and NOx were determined experimentally across a wide range of power stations and ...technologies, and compared to the IPCC default factors. It was found that the CO2 emission factors tended to be at the upper end of the IPCC default range, whereas the NOx emission factors were generally below the low end. The results from South Africa tend to dominate the regional picture at present, but this is likely to change in the near future, as Botswana has announced plans to introduce over 4 000 MWe of coal-fired power stations.
Fortunately, the Ebola outbreak has been controlled. In this final report, data on the duration of the persistence of Ebola virus in semen are provided.
The Zambezi River Basin in southern Africa is relatively undeveloped from both a hydropower and irrigated agriculture perspective, despite the existence of the large Kariba and Cahora Bassa dams. ...Accelerating economic growth increases the potential for competition for water between hydropower and irrigated agriculture, and climate change will add additional stresses to this system. The objective of this study was to assess the vulnerability of major existing and planned new hydropower plants to changes in climate and upstream irrigation demand. Our results show that Kariba is highly vulnerable to a drying climate, potentially reducing average electricity generation by 12 %. Furthermore, the expansion of Kariba generating capacity is unlikely to deliver the expected increases in production even under a favourable climate. The planned Batoka Gorge plant may also not be able to reach the anticipated production levels from the original feasibility study. Cahora Bassa’s expansion is viable under a wetting climate, but its potential is less likely to be realised under a drying climate. The planned Mphanda Nkuwa plant can reach expected production levels under both climates if hydropower is given water allocation priority, but not if irrigation is prioritised, which is likely. For both Cahora Bassa and Mphanda Nkuwa, prioritising irrigation demand over hydropower could severely compromise these plants’ output. Therefore, while climate change is the most important overall driver of variation in hydropower potential, increased irrigation demand will also have a major negative impact on downstream plants in Mozambique. This implies that climate change and upstream development must be explicitly incorporated into both project and system expansion planning.
The study presents long-term electricity supply and demand scenarios for the twelve countries in the Southern African Power Pool, based on detailed bottom-up demand analysis for all countries and a ...set of internally consistent development scenarios. Total regional electricity demand and supply increase by eight to fourteen times from 2010 to 2070, with major shifts in both the sectoral composition of demand and the geography of demand, with South Africa becoming a much smaller share. On the supply side, the fuel mix shifts from coal and toward hydro in the medium term, but towards other renewables, such as solar, in the longer term, particularly in the scenarios with the fastest decline in capital costs for renewables. This leads to declining unit carbon dioxide emissions in the more aggressive scenarios, even though total power sector emissions still increase. The unit cost of generation for the entire region is stable across all scenarios. The potential transformation of the supply sector would require a fundamental shift in resource use, grid management and infrastructure development in the region, as well as greater regional integration. This also implies significant institutional capacity development in the SAPP Coordination Centre or similar structures for cooperative management of resources.
The clinical, virologic, and immunologic findings in a female Ebola virus disease patient are described. During the long-term follow-up, Ebola virus RNA was detectable in vaginal fluid before 36 days ...after symptom onset, with nearly an identical genome sequence as in acute phase blood. Ebola-specific T cells retained activation at 56 days after disease onset.
Modern use of biomass energy has increased in many parts of the world, with the
key driving forces being soaring oil prices, commitments to address climate change
and the need for rural development ...(Faaij and Domac, 2006). A reliable supply and
stable demand of feedstocks are always required as a prerequisite to sustainable
market development. The exploitable bioenergy potential of the sub-Saharan Africa
region is significant and is estimated to be the highest of any world region (Smeets
et al., 2007).
Sugar cane has become an important source of bioenergy globally, and at the
same time, the sugar industry has entered a period of transition. Subsidies within the
European Union have been reduced, preferential market access to the African, Caribbean and Pacific (ACP) countries has been adjusted and prices and quotas for least
developed countries (LDCs) are somewhat more constrained (Innes, 2010). There
will remain, however, a considerable amount of preferential market access for sugar,
so that the “free market” where world commodity prices apply will remain “thin”
for some years to come (Alvarez and Polopolus, 2008; Chapter 8 in this Volume).
Two important co-products of the sugar cane industry are cogenerated electricity from bagasse and bioethanol. While the former may only have a domestic and
regional market, bioethanol has an additional opportunity on international markets
that can be exploited (Johnson and Matsika, 2006). The possibility for African
LDCs to export ethanol to the EU has been recognized due to the fact that EU
countries must meet mandates under the Renewable Energy Directive (EC, 2009),
while at the same time many LDCs are exempt from agricultural import tariffs
applied to products such as bioethanol (see Chapter 8).
The main driving forces for market diversification into renewable energy include
uncertainties in oil and sugar prices, land and resource availability, power supplyconditions, environmental policies and economic development policies. The challenges to diversification include lack of supporting national and international policies, difficulties with market access and technological constraints, as well as the
more general barriers that stifle the development of renewable energy sources. This
chapter will consider the implementation strategies available to sugar producers and
the policy incentives that can stimulate greater production of renewable energy
from sugar cane. The emphasis will be on bioethanol and cogeneration, although
some of the same approaches can support other energy and non-energy products or
markets that use biomass from sugar cane.
PDF
