Total Site Level Research Articles

Stratified burn severity assessment by integrating spaceborne spectral and waveform attributes in Great Xing'an Mountain

Burn severity assessment is critical for understanding the pattern of post-fire vegetation recovery and ecosystem resilience. Previous studies proposed various field criteria (e.g., Composite Burn Index (CBI)) to quantify burn severity from strata level to total site level, yet suffering from surveyors' subjective interpretation across site conditions. High-resolution passive remote sensing allows for more objective assessment based on the strong relation between fire damages and spectral features. Importantly, burn severity generally characterizes differences between forest overstory and understory layers due to their discrepancies in vegetation structures and environmental conditions. Spatially explicit mapping of strata-level burn severity is vital for post-fire forest management and ecological function evaluation. Until now, almost no available spaceborne remote sensing method can concurrently assess overstory and understory burn severity over heterogeneous forests. In this study, we proposed a Hybrid Composite Burn Index (HCBI) that comprehensively indicates the fire-induced spectral and structural changes along the vertical profile by integrating spectral and waveform attributes from both active and passive remote sensing data. Firstly, we introduced two remote sensing-based rating factors namely relative spectral change (RSC) and relative waveform change (RWC), and established HCBI through weighting and scoring the rating factors. Subsequently, we evaluated the effectiveness and generality of overstory, understory, and total site HCBI based on various pairs of simulated remote sensing data of pre-fire and post-fire forest scenes. Thirdly, we derived the spatially discontinuous maps of overstory, understory, and total site HCBI of the Xiushan fire site in Great Xing'an Mountain using WorldView-2 (WV-2) multispectral imagery and Global Ecosystem Dynamics Investigation (GEDI) full-waveform LiDAR data. Finally, we produced wall-to-wall HCBI maps using multiple predictive variables from pre-fire and post-fire Sentinel-2 MultiSpectral Instrument (MSI) images with a Random Forest (RF) algorithm. The predicted overstory, understory, and total site HCBI were validated by field-surveyed CBI. The assessment results based on simulation data showed HCBI was sensitive to the fire damage regardless of burn severity levels and vegetation cover levels (R2 of larger than 0.97 and RMSE of <0.15). The prediction results based on RF models achieved reliable HCBI of the total site, overstory, and understory levels (R2 of around 0.85 and RMSE of around 0.30). We found the wall-to-wall maps of HCBI captured the subtle horizontal and vertical variation even in the case of understory burn alone. We concluded that the newly proposed HCBI can advance the remote sensing-based assessment of stratified burn severity, offering opportunities for making fine-scale forest management decisions.

Targeting for Energy Efficiency and Improved Energy Collaboration Between Different Companies Using Total Site Analysis (TSA)

A chemical cluster located in Stenungsund on the West Coast of Sweden is analyzed to determine the total site level energy efficiency opportunities using the Total Site Analysis (TSA) method. The cluster consists of 5 chemical companies, i.e., AGA Gas AB producing industrial gases, Akzo Nobel Sverige AB producing amines and surfactants, Borealis AB producing ethylene, and PE, INEOS Sverige AB producing PVC and Perstorp Oxo AB producing speciality chemicals. The heart of the cluster is a steam cracker plant run by Borealis, which delivers partly feedstock and fuel to the other plants. The overall heating and cooling demands of the site are ∼ 442 and 953 Mw, respectively. TSA is used to stepwise design a site-wide utility system which improves energy efficiency. Utility savings of ≤ 122 Mw can be achieved, plus a steam excess of 7 Mw. Qualitative evaluation of the suggested measures shows that 60 Mw of the savings potential can be expected to be achieved with moderate changes to the process utility system. This is an abstract of a paper presented at the 19th International Congress of Chemical and Process Engineering and 7th European Congress of Chemical Engineering (Prague, Czech Republic 8/28/2010-9/1/2010).

Procedure for the Simultaneous Synthesis of Heat Exchanger Networks at Process and Total Site Level

Although Heat Exchanger Network (HEN) synthesis methods have been in existence for forty years, several issues still need to be resolved in order to obtain more realistic networks. Moreover, the complexity of the problem further increases when Heat Integration is performed at the Total Site level rather than at the process level. The usual approach is first to perform Heat Integration within the processes, and later to consider the non-integrated parts for Total Site Heat Integration. This sequential approach can omit some promising solutions and thus generally leads to worse results compared to the approach where the entire Total Site is synthesized simultaneously (Nemet et al., 2014). In order to obtain more realistic results, several practical constraints should be accounted for, such as transport between processes, optimal intermediate utility temperature level(s), pipeline design, heat losses and pressure drop (Nemet et al., 2015).In this work a synthesis of the Total Site is performed, which simultaneously considers integration within and between plants (at the plant and at the Total Site levels). For this purpose, the superstructure optimization approach is used. The superstructure contains all the possible matches for heat exchange within and between processes. Heat exchange between processes can be performed in the following ways: i) directly, by exchanging heat between the hot stream of one process and the cold stream of another process, or ii) indirectly, by utilizing an intermediate utility at optimal temperature levels (these are optimization variables). In both cases the transport of the heat carrier, either the process stream or the intermediate utility stream, is considered. Because there are severe nonlinearities and numerous options for heat recovery, the model is difficult to implement even for small-scale problems. However, when evaluating potential matches, it usually happens that most matches are either infeasible given heat transfer limitations, or unviable for economic reasons. A two-step approach is therefore proposed, where in the first step match alternatives are pre- screened with respect to infeasibility and unviability, and in the second step, a more detailed design is synthesized, taking into consideration the reduced superstructure obtained in the first step. The proposed two- step procedure yields results simultaneously at both the process and the Total Site levels, while also accounting for important properties such as heat losses, pipeline design and cost, temperature/pressure drop during transport between processes, and different types of heat exchangers.

Data Reconciliation for Total Site Integration

Data reconciliation is one of the important steps in Heat Exchanger Network (HEN) retrofit. Correctly performed data reconciliation can help in Heat Integration (HI) analysis. In this work, iterative method for reconciling heat exchanger network HI is explored. This work addresses the limitation encountered by the iterative method previously published. Several solution strategies have been evaluated. The work also proposes a procedure for data reconciliation at Total Site level. An illustrative case study shows the effectiveness of this iterative method. The iterative method provides a relatively good result, when compared with simultaneous method.

Minimum heat transfer area for Total Site heat recovery

In this paper a further development of methodology for decreasing the capital cost for Total Site heat recovery by use of different utility levels is proposed. The capital cost of heat recovery system is estimated for certain temperature level of intermediate utility applying Total Site Profiles. Heat transfer area is reduced by selection of appropriate temperature of intermediate utility. Minimum of heat transfer area depends on slopes of Total Site Profiles in each enthalpy interval. This approach allows estimating the minimum of heat transfer area for heat recovery on Total Site level. Case study is performed for fixed film heat transfer coefficients of process streams and intermediate utilities. It indicates that the total heat transfer area of heat recovery can be different up to 49.15% for different utility temperatures.

Total site methodology as a tool for planning and strategic decisions

A Total Site (TS) is defined as a set of processes (industrial plants, residential, business and agriculture units) linked through the central utility system. The utility system incorporates a number of operating units such as boilers, steam turbines, gas turbines and letdown stations. Many sites are using the TS system representation. Heat Integration at TS level has been well developed and successfully implemented. However, sites typically develop with time and even minor changes/extensions can affect TS heat recovery significantly. It is beneficial to plan their strategic development in advance, to increase or at least not to decrease the rate of heat recovery when integration of additional processes takes place. Even when this has not been done at the initial stage, the TS methodology can still be used as a tool for the strategic planning decision making. This work illustrates how the TS methodology can contribute to the strategic development and the extension planning of already existing TS. The aim is to reveal the potentials for Heat Integration, when new units or processes are considered for the inclusion in the TS. Moreover, some operating parameters (e.g. temperature or capacity) of the unit can be proposed to achieve the best possible heat recovery. The degrees of freedom for TS changes can be on two levels: (i) only adding an operating unit to the current utility system (the Total Site Profiles remain the same) or (ii) changing of the TS by including more processes (the Total Site Profiles are changed). The first group of changes includes the integration of heat engines to produce electricity utilising heat at higher temperature and returning it to the system at lower temperature, which is still acceptable for the heat recovery and simultaneously for the electricity production. The second group of changes is more complex. For evaluating these changes a plus/ minus principle is developed allowing the most beneficial integration of new units to the TS. Combinations of both types of changes are also considered.

Capital Cost Targeting of Total Site Heat Recovery

Exploiting heat recovery on Total Site level offers additional potential for energy saving through the central utility system. In the original Total Site Methodology (Klemes et al., 1997) a single uniform ΔTmin specification was used. It is unrealistic to expect uniform ΔTmin for heat exchange for all site processes and also between processes and the utility system. The current work deals with the evaluation of the capital cost for the generation and use of site utilities (e.g. steam, hot water, cooling water), which enables the evaluation of the trade-off between heat recovery and capital cost targets for Total Sites, thus allowing to set optimal ΔTmin values for the various processes. The procedure involves the construction of Total Site Profiles and Site Utility Composite Curves and the further identification of the various utility generation and use regions at the profile-utility interfaces. This is followed by the identification of the relevant Enthalpy Intervals in the Balanced Composite Curves. A preliminary result for evaluation of heat recovery rate and capital cost can be obtained.

Targeting for cogeneration potential through total site integration

Total site integration offers energy conservation opportunities across different individual processes and also to design as well as to optimize the central utility system. In total site integration of the overall process, indirect integration with intermediate fluids or through a central utility system are preferred as it offers greater advantages of flexibility and process control but with reduced energy conservation opportunities. To achieve the maximum possible indirect integration between processes assisted heat transfer, i.e., heat transfer outside the region between process pinch points, plays a significant role. A new concept is proposed in this paper for total site integration by generating a site level grand composite curve (SGCC). Proposed SGCC targets the maximum possible indirect integration as it incorporates assisted heat transfer. In this paper, a methodology is proposed to estimate the cogeneration potential at the total site level, utilizing the concept of multiple utility targeting on the SGCC. The proposed methodology to estimate the cogeneration potential is simple and linear as well as utilizes the rigorous energy balance at each steam header.

Genetic structuring of the stream lily Helmholtzia glaberrima (Philydraceae) within Toolona Creek, south-eastern Queensland

The distribution of genetic variation among five isolated sites of the riparian species Helmholtzia glaberrima (J.D.Hook) was examined in Toloona Creek (28�13′S, 153�07′E) by using dominant amplified fragment length polymorphism (AFLP) markers. From the 137 fragments assessed, analysis of molecular variance (AMOVA) showed that most genetic variability occurred within sites (68%), although high (32%) variation also occurred among sites. Highly significant pairwise θ estimates among all sampled sites suggest that gene flow is restricted in H. glaberrima. Levels of within-site diversity were intermediate and significantly different across the sampled sites. Significant levels of linkage disequilibrium were detected at all sites except TC3. Differences in linkage disequilibrium and genetic diversity among the sites suggest that sites may have been founded by different numbers of colonists. Mantel tests found no correlation between geographic and genetic distance and significant levels of linkage disequilibrium were detected at the total site level, supporting a non-equilibrium model of population structure. The observed pattern of non-equilibrium population structure and genetic variation in H. glaberrima are best explained by a classical metapopulation model.