Muhammad Wakil Shahzad

Progress of adsorption cycle and its hybrids with conventional multi-effect desalination processes

AbstractThe water energy environment nexus is an important issue in today’s development of desalination for potable water production. Engineers and scientists in desalination are striving not only for more energy efficient technology, they are concern with the environment impact in terms of CO2 emissions and discharge of chemical laden brine into the sea. The complexity of available technologies dictates engineers and scientists to be aware of the environmental impact from both fundamental sciences and technology processes. The thermodynamics limit for desalination is known to have an energy consumption of 0·78 to 1·09 kWhe per m3, but practical desalination processes are operated at several folds higher than the thermodynamic limit due to irreversible losses incurred in removing dissolved salts. Although recent advances in membrane technology has an energetic benchmark of 3·5–5 kWhe m−3 or about 14·5 kWh_pe (primary energy) per m3, the high water production rates and protection of membranes have resulted...

An exergy approach to efficiency evaluation of desalination

This paper presents an evaluation process efficiency based on the consumption of primary energy for all types of practical desalination methods available hitherto. The conventional performance ratio has, thus far, been defined with respect to the consumption of derived energy, such as the electricity or steam, which are susceptible to the conversion losses of power plants and boilers that burned the input primary fuels. As derived energies are usually expressed by the units, either kWh or Joules, these units cannot differentiate the grade of energy supplied to the processes accurately. In this paper, the specific energy consumption is revisited for the efficacy of all large-scale desalination plants. In todays combined production of electricity and desalinated water, accomplished with advanced cogeneration concept, the input exergy of fuels is utilized optimally and efficiently in a temperature cascaded manner. By discerning the exergy destruction successively in the turbines and desalination processes, ...

Geothermal electricity generation and desalination: an integrated process design to conserve latent heat with operational improvements

AbstractA new process combination is proposed to link geothermal electricity generation with desalination. The concept involves maximizing the utilization of harvested latent heat by passing the turbine exhaust steam into a multiple effect distillation system and then into an adsorption desalination system. Processes are fully integrated to produce electricity, desalted water for consumer consumption, and make-up water for the geothermal extraction system. Further improvements in operational efficiency are achieved by adding a seawater reverse osmosis system to the site to utilize some of the generated electricity and using on-site aquifer storage and recovery to maximize water production with tailoring of seasonal capacity requirements and to meet facility maintenance requirements. The concept proposed conserves geothermally harvested latent heat and maximizes the economics of geothermal energy development. Development of a fully renewable energy electric generation-desalination-aquifer storage campus is...

A Universal Isotherm Model to Capture Adsorption Uptake and Energy Distribution of Porous Heterogeneous Surface

The adsorbate-adsorbent thermodynamics are complex as it is influenced by the pore size distributions, surface heterogeneity and site energy distribution, as well as the adsorbate properties. Together, these parameters defined the adsorbate uptake forming the state diagrams, known as the adsorption isotherms, when the sorption site energy on the pore surfaces are favorable. The available adsorption models for describing the vapor uptake or isotherms, hitherto, are individually defined to correlate to a certain type of isotherm patterns. There is yet a universal approach in developing these isotherm models. In this paper, we demonstrate that the characteristics of all sorption isotherm types can be succinctly unified by a revised Langmuir model when merged with the concepts of Homotattic Patch Approximation (HPA) and the availability of multiple sets of site energy accompanied by their respective fractional probability factors. The total uptake (q/q*) at assorted pressure ratios (P/Ps) are inextricably traced to the manner the site energies are spread, either naturally or engineered by scientists, over and across the heterogeneous surfaces. An insight to the porous heterogeneous surface characteristics, in terms of adsorption site availability has been presented, describing the unique behavior of each isotherm type.

An Improved Cost Apportionment for Desalination Combined with Power Plant: An Exergetic Analyses

In this paper an improved method for fuel cost apportionment of a combined power cum a desalination plant is presented. The conventional analysis for cogeneration systems has been, hitherto, the energetic (enthalpy) method which is useful for efficiency evaluation purposes, but it may not be fully accurate for capturing the “quality of fuel energy” consumed by processes in producing two or more useful effects, e.g., electricity and water. An exergy destruction procedure is proposed for the cost apportionment of fuel energy consumed where the available work potential of expanding stream can be fully accounted for cost distribution of the designed processes. For example, the turbines, that is used for power generation, exploits mainly the sensible-energy changes of high enthalpy steam undergoing expansion at high pressures and temperatures, whilst the thermally-activated desalination processes, such as the multi-effect distillation (MED), needed only the high latent-heat of bled-steam but at low pressures that has negligible work potential if the steam were to be used in the turbines. From this analysis, the incurred exergy destruction by the desalination processes is only 2%-7% of the total destruction available to the plant with bled-steam up to 50% of the total flow. We examined the ratio of exergy destruction consumed by the water to power production and, such a ratio is used as a basis for the fuel-cost determination in the cogeneration plant. It captures not only the realistic exergetic value of bled-steam of MED desalination, but it exposes the major shortcomings of the conventional enthalpy changes where a disproportion share of the input fuel cost, up to 32% of the total fuel input, may have been erroneously apportioned and giving an unfair valuation of the operational water cost.

Future Energy Benchmark for Desalination: Is it Better to have a Power (Electricity) Plant With RO or MED/MSF?

Power and desalination cogeneration plants are common in many water scared courtiers. Designers and planners for cogeneration face tough challenges in deciding the options:- Is it better to operate a power plant (PP) with the reverse osmosis (i.e., PP+RO) or the thermally-driven multi-effect distillation/multi-stage flashed (PP+MED/MSF) methods. From literature, the RO methods are known to be energy efficient whilst the MED/MSF are known to have excellent thermodynamic synergies as only low pressure and temperature steam are used. Not with-standing the challenges of severe feed seawater of the Gulf, such as the frequent harmful algae blooms (HABs) and high silt contents, this presentation presents a quantitative analyses using the exergy and energetic approaches in evaluating the performances of a real cogeneration plant that was recently proposed in the eastern part of Saudi Arabia. We demonstrate that the process choice of PP+RO versus PP+MED depends on the inherent efficiencies of individual process method which is closely related to innovative process design. In this connection, a method of primary fuel cost apportionment for a co-generation plant with a MED desalination is presented. We show that an energy approach, that captures the quality of expanding steam, is a better method over the conventional work output (energetic) and the energy method seems to be over-penalizing a thermally-driven MED by as much as 22% in the operating cost of water.

Experimental Study of a Laminar Flow Solid Desiccant Dehumidifier Driven by a Low Temperature Heat Source

In this paper, an experimental study of a laminar flow solid desiccant dehumidifier has been presented. The cyclic steady state performance of adsorption-desorption processes was analyzed at various heat source temperatures and typical ambient humidity conditions in tropics. The desiccant dehumidification system consists of two beds filled with silica gel, two heat exchangers operating at 30 oC and 80 oC respectively, three humidity stations for measurement of the temperature and humidity conditions of the system and a blower to make airflow throughout the system. Type-RD silica gel of 0.3 mm average diameter was used as the working desiccant in the dehumidification system. This system has no moving parts rendering less maintenance compared with a rotary type. It is also energy-efficient means of dehumidification by adsorption process with low temperature heat source as compared to the conventional methods. As a result, it was observed the humidity ratio of inlet air is reduced from 24 g/kg of dry air to about 17 g/kg of dry air. Concomitantly, hot water at 80 oC is used to regenerate the adsorbent.

Adsorption Cycle and Its Hybrid with Multi-Effect Desalination

Adsorption (AD) cycle is recently pioneered for cooling and desalination applications. For water treatment, the cycle can be used to treat highly concentrated feed water, ranging from seawater, ground water, and chemically laden waste water. This chapter presents a review of the recent development of AD cycle and its hybridization with known conventional cycles such as the MED and MSF. We begin by looking at the basic sorption theory for different adsorbent–adsorbate pairs, namely the silica gel– water and the zeolite–water pairs. Under the IUPAC categorization, there are six types of isotherm behavior that capture almost all types of adsorbent–adsorbate behaviors and many isotherm correlations have been developed to described their uptake patterns, namely the Henry, Langmuir, Toth, etc. We have recently developed a correlation that can universally capture all six types of isotherms of IUPAC and it requires only four regression coefficients. We present also the basic AD cycle for seawater desalination as well as its hybridiza‐ tion with known conventional thermally driven cycles. We present the performances of the AD pilot which was powered by renewable solar thermal input. Owing to thermodynamic synergy between the thermally driven cycles, the AD cycle is combined with the robust multi-effect distillation cycle to improve the water production yields. The hybrid cycle is called the “MED+AD” or MEDAD in short. With hybridization, it allows the bottom-brine temperature of the MED to operate below ambient temperature, as low as 5°C, in contrast to the conventional MED which is limited by the ambient, resulting in a quantum increase of distillate production by two to three times. We demonstrate this efficiency improvement in a pilot comprising

Thermo-Mechanical Investigation of Free Volume Theory for Polyamie-6

Polymers always show time-dependent mechanical properties. In order to use polymers in engineering applications, long-term mechanical propertes should be characterized. Free volume theroy is the mostly used theory to predict and model the mechanical properties of polymers. The effect of temperature is modelled thorugh William-Landel-Ferry (WLF) equation, whereas, the combined effect of temperature and pressure is modelled by Filler-Moonan-Tschoegl (FMT) equation. Both of the models are based on free volume theory. A set of expermentations were performed to investigate the validity of free volume concpet for one of the most important engineering polymer; i.e. Polyamide-6.