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

Total site targeting with stream specific minimum temperature difference

The paper focuses on extending traditional Total Site Integration methodology to produce more meaningful utility and heat recovery targets for the process design. The traditional methodology leads to inadequate results due to inaccurate estimation of the overall Total Site heat recovery targets. The new methodology is a further development of a recently extended traditional pinch methodology. The previous extension was on the introduction of using an individual minimum temperature difference (δTmin) for different processes so that the δTmin is more representative of the specific process. Further this paper deals with stream specific δT min inside each process by setting different δT contribution (δTcont) and also using different δTcont between the process streams and the utility systems. The paper describes the further extended methodology called stream specific targeting methodology. A case study applying data from a real diary factory is used to show the differences between the traditional, process specific and stream specific total site targeting methodologies. The extended methodology gives more meaningful results at the end of the targeting with this avoiding the over or under estimated heat exchanger areas in the process design

Hitting time for the continuous quantum walk

We define the hitting (or absorbing) time for the case of continuous quantum walks by measuring the walk at random times, according to a Poisson process with measurement rate $\lambda$. From this definition we derive an explicit formula for the hitting time, and explore its dependence on the measurement rate. As the measurement rate goes to either 0 or infinity the hitting time diverges; the first divergence reflects the weakness of the measurement, while the second limit results from the Quantum Zeno effect. Continuous-time quantum walks, like discrete-time quantum walks but unlike classical random walks, can have infinite hitting times. We present several conditions for existence of infinite hitting times, and discuss the connection between infinite hitting times and graph symmetry.Comment: 12 pages, 1figur

Decomposing generalized measurements into continuous stochastic processes

One of the broadest concepts of measurement in quantum theory is the generalized measurement. Another paradigm of measurement--arising naturally in quantum optics, among other fields--is that of continuous-time measurements, which can be seen as the limit of a consecutive sequence of weak measurements. They are naturally described in terms of stochastic processes, or time-dependent random variables. We show that any generalized measurement can be decomposed as a sequence of weak measurements with a mathematical limit as a continuous stochastic process. We give an explicit construction for any generalized measurement, and prove that the resulting continuous evolution, in the long-time limit, collapses the state of the quantum system to one of the final states generated by the generalized measurement, being decomposed, with the correct probabilities. A prominent feature of the construction is the presence of a feedback mechanism--the instantaneous choice weak measurement at a given time depends on the outcomes of earlier measurements. For a generalized measurement with $n$ outcomes, this information is captured by a real $n$-vector on an $n$-simplex, which obeys a simple classical stochastic evolution.Comment: 9 pages, LaTeX, name changed, typos correcte

Total site heat integration of multi-effect evaporators with vapour recompression for older kraft mills

This paper aims to apply Total Site Heat Integration (TSHI) to appropriately integrate Mechanical and Thermal Vapour Recompression with multi-effect evaporators at older Kraft Mills, to cause a step reduction in fossil fuel use and its associated emissions. Heat and power demands for older Kraft Mills are chiefly satisfied from Recovery Boilers (RB), heavily supplemented by biomass/fossil fuel boilers, and integrated with steam turbines. Prior to firing, black liquor - the RB fuel - is concentrated from about 18 % to 67 % in a multi-effect evaporator, which demands 20 % of site-wide thermal energy. With access to renewable electricity, this study finds that vapour recompression can be economically integrated into a multi-effect evaporator at older Kraft Mills. The vapour recompression configuration with the greatest economic potential used 2-stages of mechanical vapour recompression and 1-stage of thermal vapour recompression. This system achieved a levelised profit of NZD 8.56 M/y, a payback period of 1.0 y and an internal rate of return of 103 %. An optimum integrated set-up needs to account for site-specific heat demand and utility supply profiles through TSHI

Innovative hybrid heat pump for dryer process integration

This study aims to simulate and optimise a hybrid compression-absorption heat pump process for convective dryers considering Pinch design principles. With a greening electricity grid, heat pumps represent an effective technology to reduce process heat emissions. As a result, numerous types of heat pumps integrated with convective dryers have been reported in the literature, but no study was found to use a hybrid heat pump. To simplify the design and optimisation, Process Integration principles for compressors and expanders from literature are synthesised into a Pinch design method for heat pumps. A milk spray dryer case study is analysed. Simulation results using Petro-Sim™ show that the optimally design hybrid heat pump system can reduce dryer energy demand by 47.3 % and total emissions by 42.4 % (assuming a low carbon electricity grid) while achieving a gross Coefficient of Performance of 4.53. Future work will look at optimising the selection and composition of working fluid for the hybrid heat pump system as well as investigating the economics of its implementation in industry

SYNTHESIS AND STUDY OF THE MATHEMATICAL MODEL OF A TRICOPTER

Abstract: In this report is synthesized and studied the mathematical model of a tricopter. The stabilization of a tricopter in angular velocity and angle is presented