CHEMICAL COAL DESULPHUR1ZATION RESEARCH IN TURKEY

Abstract

A number of methods have been developed which are used to remove the sulphur present in coal before combustion. The physical removal of pyritic sulphur by coal cleaning has been commercial practice for a number of years, but these methods do not remove organically bound sulphur, they can be applied effectively only to a limited number of coals. However, the removal of both pyritic and organically bound sulphur from coal can be effectively achieved by applying the chemical desulphurization methods. This paper gives a general review on the chemical desulphurization studies, including carbonization in different atmospheres, air oxidation, wet oxidation, Meyers Process, chlorination and extraction with the solutions of NaOH, CuCl₂ and C₂H₅OH, which were carried out using different Turkish lignites.     

Joint quantity flexibility for multiple products in a decentralized supply chain

In this study, we analyze a decentralized supply chain with a single retailer and a single manufacturer where the retailer sells multiple products in a single period. The products differ in terms of a limited number of features only. The retailer places initial orders based on preliminary demand forecasts at the beginning of the period and has an opportunity to modify its initial order after receiving perfect demand information. However, the final orders of the retailer are constrained by its initial orders. The manufacturer has two options for procurement. The first procurement option is regular delivery at the beginning of the period, after the initial orders of the retailer. The next one is expedited delivery, after the updated orders are received. In this setting, our objective is to characterize the optimal policies for the retailer and the manufacturer, and assess the benefits of flexibility.     

Characterization of poly(vinylferrocenium) coated surfaces and their applications in DNA sensor technology

Poly(vinylferrocenium) (PVF⁺) modified gold (Au) electrode was developed in this study for the electrochemical sensing of deoxyribonucleic acid (DNA) hybridization based on the oxidation signals of polymer and guanine, and also for the electrochemical investigation of interaction of anticancer drug, mitomycin C (MC) and DNA immobilized onto PVF⁺ modified Au electrode. PVF⁺ modified Au electrode was prepared by electrooxidation of poly(vinylferrocene) PVF at +0.7 V versus Ag/AgCl reference electrode. The polymer modified electrode and DNA immobilized polymer modified electrode were characterized by X-ray photoelectron (XPS), Fourier transform infrared-attenuated total reflentance (FTIR-ATR) and alternating current (AC) impedance spectroscopy. For application studies, differential pulse voltammetry (DPV) technique was used.     

Mechanical performance of low cement reactive powder concrete (LCRPC)

The possibility of producing a reactive powder concrete (RPC) with low cement content was aimed in the scope of this study. Cement was replaced with class-C fly ash (FA) up to 60% for this purpose. Three different curing conditions (standard water curing, autoclave curing and steam curing) were applied to specimens. Two series of RPC composites were prepared with bauxite and granite aggregates. Mechanical properties such as compressive strength, splitting tensile strength, flexural strength and fracture energy of composites were investigated. Test results showed that, compressive strength of 200 MPa can be reached with low cement by using high-volume fly ash. Thermally treated specimens showed compressive strength beyond 250 MPa and high volume fly ash RPC have superior performance. Furthermore, compressive strength values reached up to 400 MPa with external pressure application during setting and hardening stages.     

Optimal control of LTI systems over unreliable communication links

In this paper, optimal control of linear time-invariant (LTI) systems over unreliable communication links is studied. The motivation of the problem comes from growing applications that demand remote control of objects over Internet-type or wireless networks where links are prone to failure. Depending on the availability of acknowledgment (ACK) signals, two different types of networking protocols are considered. Under a TCP structure, existence of ACK signals is assumed, unlike the UDP structure where no ACK packets are present. The objective here is to mean-square (m.s.) stabilize the system while minimizing a quadratic performance criterion when the information flow between the controller and the plant is disrupted due to link failures, or packet losses. Sufficient conditions for the existence of stabilizing optimal controllers are derived.     

Design of PI controllers for achieving time and frequency domain specifications simultaneously

This paper deals with the design of PI controllers which achieve the desired frequency and time domain specifications simultaneously. A systematic method, which is effective and simple to apply, is proposed. The required values of the frequency domain performance measures namely the gain and phase margins and the time domain performance measures such as settling time and overshoot are defined prior to the design. Then, to meet these desired performance values, a method which presents a graphical relation between the required performance values and the parameters of the PI controller is given. Thus, a set of PI controllers which attain desired performances can be found using the graphical relations. Illustrative examples are given to demonstrate the benefits of the method presented.     

Electrosynthesis of benzoquinone from phenol on α and β surfaces of PbO2

Electrosynthesis of benzoquinone from phenol was investigated in acetonitrile-water mixtures on α-PbO₂ and β-PbO₂ electrodes. The influence of water concentration, electrolysis potential, initial phenol concentration and temperature on benzoquinone production was also studied. Different electrocatalytic activities of α and β structures of PbO₂ were determined.     

Runtime verification of concurrency-specific correctness criteria

We give an overview of correctness criteria specific to concurrent shared-memory programs and runtime verification techniques for verifying these criteria. We cover a spectrum of criteria, from ones focusing on low-level thread interference such as races to higher-level ones such as linearizability. We contrast these criteria in the context of runtime verification. We present the key ideas underlying the runtime verification techniques for these criteria and summarize the state of the art. Finally, we discuss the issue of coverage for runtime verification for concurrency and present techniques that improve the set of covered thread interleavings.     

Unsteady flows of a binary mixture of incompressible Newtonian fluids in an annulus

This paper is concerned with applying the mixture theory of two chemically inert incompressible Newtonian fluids to some simple unsteady flows in the annular region between two infinitely long coaxial cylinders. The equations governing the motion of the binary mixture under discussion are reduced to a system of coupled partial differential equations. With the help of finite Hankel transforms, the exact solutions of these equations are obtained in series form for the following three problems: (i) unsteady axial Couette flow in an annulus, (ii) unsteady Poiseuille flow in an annulus, (iii) unsteady circular Couette flow in an annulus.