Heat Pumps in Chemical Process Industry

Anton A. Kiss, Carlos A. Infante Ferreira

• Publisher: CRC Press
• Year: 2016
• ISBN:
  9781498719032
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Industrial & Technical Chemistry

As the chemical process industry is among the most energy demanding sectors, chemical engineers are endeavoring to contribute towards sustainable future. Due to the limitation of fossil fuels, the need for energy independence, as well as the environmental problem of the greenhouse gas effect, there is a large increasing interest in the research and development of chemical processes that require less capital investment and reduced operating costs and lead to high eco-efficiency. The use of heat pumps is a hot topic due to many advantages, such as low energy requirements as well as an increasing number of industrial applications. Therefore, in the current book, authors are focusing on use of heat pumps in the chemical industry, providing an overview of heat pump technology as applied in the chemical process industry, covering both theoretical and practical aspects: working principle, applied thermodynamics, theoretical background, numerical examples and case studies, as well as practical applications. The worked-out examples have been included to instruct students, engineers and process designers about how to design various heat pumps used in the industry. Reader friendly resources namely relevant equations, diagrams, figures and references that reflect the current and upcoming heat pump technologies, will be of great help to all readers from the chemical and petrochemical industry, biorefineries and other related areas.

CHAPTER 1

Introduction to Heat Pumps

1.1INTRODUCTION

A heat pump (HP) is a device that transfers energy from a heat source to a heat sink (destination) and upgrades the energy to a higher temperature level. Heat pumps are designed to move heat in the opposite direction of normal heat flow by taking heat from a colder space and releasing it to a warmer one. Although the overall process seems to allow the heat to flow from the cold source to the warm destination, the normal heat flow from high to low temperature is respected in each step of the process. Note that a heat pump uses a certain amount of work (external power) to accomplish the transfer of energy from the heat source to the heat sink.

The most common examples are refrigerators, air conditioners (ACs) and reversible-cycle heat pumps for providing thermal comfort. Notably, the term heat pump is more generic; it applies to many heating, ventilating and air conditioning (HVAC) devices used for space heating or cooling. When used for heating, a heat pump employs the same refrigeration-type cycle used by an air conditioner, but in the opposite direction – thus drawing heat from the ground or external air and releasing the heat into the air-conditioned space rather than the surrounding environment.

Heat pumps have several key advantages: very high efficiency as compared to gas-heated systems; the possibility to use environmental renewable energy from the air, water or ground; large energy savings of 50%–70% translated in reduced final and primary energy demand and significant reductions in greenhouse gas (GHG) emissions (e.g. CO₂). Nonetheless, heat pumps also have some drawbacks: An initial investment is needed (so payback times might be an issue), an electrical connection is required to be present typically and some refrigerants used in a heat pump are toxic or flammable (health, safety, environment [HSE] issues). It is worth noting that the investment costs of a heat pump depend strongly on the application type and location, being influenced by several key factors: required temperature (higher temperature requires expensive components), required heat capacity (higher capacity needs more expensive installation), number of installations (build a number of small installations or one large installation) or available space to connect a heat pump to an existing installation (especially in an existing chemical plant).

The next sections give a historical perspective on the developments of heat pumps and describe the working principle and fundamentals, performance limitations and major types of heat pumps and their use in HVAC applications as well as in the chemical process industry (CPI).

1.2Historical Perspective

While heating has been no secret to humankind ever since the discovery and use of fire, the problem of artificial cooling was more complex. With the exception of evaporative cooling, there was no possibility for artificial cooling until about 150 years ago. Natural ice was transported on a global scale, but due to shortage problems, the heat pump development priority was on the refrigeration side. The problem of artificial cooling was not solved before about 1850, when the first refrigeration machines were invented. Of course, the same machines can be also used as heat pumps for heating. Yet, the huge demand for cooling was mainly responsible for the rapid development of heat pumps and their spread around the globe. Nowadays, over 130 million heat pumps for cooling and heating are in operation worldwide, so the importance of heat pump technologies is undeniable.

The scientific approach to heat pump technologies started with Carnot [1824], who was the first to establish a precise relationship between heat and work. Carnot’s ideas were reformulated later by Clausius [1850], but the basic statement is that mechanical energy may be transformed completely into heat energy, but that heat energy may be only partially transformed into mechanical energy.

Other contributions came from von Mayer, who established the principle of equivalence between work and heat [1842]; Joule, who gave the experimental proof of the principle [1843] and von Helmholtz, who expressed the principle of conservation of energy in general terms [1847] – hence firmly establishing the first law of thermodynamics. Considered one of the key founders of thermodynamics, Clausius restated Carnot’s principle (known as the Carnot cycle), thus proving the sound basis of the theory of heat. Also, Clausius was the first to state the basic ideas of the second law of thermodynamics [1850] and later explicitly introduced the concept of entropy [1865].

Independently of Clausius, Lord Kelvin derived a more general formula for the second principle [1851] and introduced the thermodynamic scale of temperature [1852]. Also, Kelvin [1852] remarked that a reverse heat engine could be used not only for cooling but also for heating and pointed out that such a heating device would need less primary energy due to the extraction of heat from the environment. Later, Boltzmann [1866] linked the concepts of entropy and probability in statistical physics, thus clarifying the Carnot principle, knowing that entropy represents the degree of disorder. Gibbs introduced enthalpy into theoretical thermodynamics [1873–1878], while Mollier brought it into applied thermodynamics [1902], using it as one co-ordinate (along with entropy or pressure) of his thermodynamic diagrams. These diagrams provided a graphic visualization and an easy method of calculation for the vapor compression (VC) cycle.

The concept of exergy – defined as the work that would be delivered by a reversible process that would bring the flow in equilibrium with the environmental conditions, this process consisting of an isentropic expansion to environment pressure and an isothermal expansion to the entropy state of the environment – was derived from the ideas of Zeugner [1859] and Lorenz [1896] and was taken up again by Bosnjakovic [1935] and after 1950 by Grassmann and Nesselmann. On the basis of a thermodynamic comparison, Linde [1870] pointed out that the compression system is more efficient than systems based on the absorption system and other principles. In addition, Swarts is widely considered as establishing the foundations of organofluorine chemistry by his work on aliphatic fluorocarbons [1890–1893]. Altenkirch [1910] carried out a study of binary mixtures for absorption refrigeration machines, and the two-stage machine had very good output. Other key contributions to the development of heat pumps include the first VC machine by Perkins [1834], first commercially successful ammonia absorption cooling system and introduction of ammonia as a refrigerant by Carré [1851], first commercial ice-making plant by Twining [1855], first pilot heat pump for heating only by von Rittinger [1855–1857], first thermostatically controlled refrigeration system by van der Weyde [1870], diffusion-absorption cycle by Geppert [1899], rolling piston rotary compressor by Rolaff [1920], plate heat exchanger by Seligman [1923], thermostatic expansion valve by Diffinger [1923], and capillary tube refrigerant control by Carpenter [1927], as well as the introduction of new refrigerants such as dimethyl ether [Tellier, 1863], carbon dioxide [Lowe, 1866], sulphur dioxide [Pictet, 1874], methyl chloride [Vincent, 1878]; chlorofluorocarbon (CFC) refrigerants [Midgley, Henne and McNary, 1928] and hydrofluorocarbon refrigerants [Henne, 1936].

During the industrialization period [1876–1918], demo units were replaced with more reliable and optimized machines to take advantage of scientific advancements and manufacturing ability. The refrigeration systems started to become industrial products on a large scale, and Linde played the...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright
• Table of Contents
• Preface
• Authors
• Chapter 1 ◺ Introduction to Heat Pumps
• Chapter 2 ◺ Thermodynamics of Heat Pump Cycles
• Chapter 3 ◺ Entropy Production and Exergy Analysis
• Chapter 4 ◺ Pinch Analysis and Process Integration
• Chapter 5 ◺ Selection of Heat Pumps
• Chapter 6 ◺ Mechanically Driven Heat Pumps
• Chapter 7 ◺ Thermally Driven Heat Pumps
• Chapter 8 ◺ Solid-State Heat Pumps
• Chapter 9 ◺ Industrial Applications of Heat Pumps
• Chapter 10 ◺ Case Studies
• Index