Zuccato Energia - Model ZE-100-LT - 100-KWE, Skid-Mounted, Low-Temperature Organic Rankine Cycle (LT-ORC) Energy Production Module

The working fluid - a low-boiling, biodegradable, non toxic liquid when at room temperature - boils in the evaporator at a temperature far lower than that of water, becoming a high-pressure dry gas which spins through its expansion the impeller of a specifically designed and sized turbine [3].

The high-speed rotation (12.000÷18.000 Rpm) of the turbine shaft spins the rotor of a generator which is directly connected to it, thus producing electric power [4] which, after being synchronized in frequency, phase and voltage by a power converter, may be injected into the national power grid or self-consumed, according to local needs and policies.

Downstream the turbine, the working fluid - still in gas phase - is conveyed to another heat exchanger, called a condenser (5), where it is cooled, releasing its excess heat and condensing back into a liquid which is collected in a condensation tank, ready to be sent back to the primary heat exchanger by a recirculation pump, thus closing the loop.

Excess heat released in the condenser is a low-temperature thermal energy source itself, which may be used for other purposes such as preheating or dessiccating biomass fuel (thus increasing its heating value), building heating, hot water production and so on.

In case that is not possible, residual heat may be dissipated by using an external cooling system [6] such as an evaporative cooling tower or a dry cooler.

Independently designed and manufactured using the most advanced technologies in finite elements and fluid-dynamics analysis (CFD/CFX), ZE turbogenerators are designed from scratch to operate in a low-temperature organic Rankine cycle which uses a special working fluid that offers better performances and several advances over traditional steam turbines:

• Low operational temperature which allow our systems to tap even low-grade heat sources;
• High condensation temperature which may allow the use of simple air-cooled condensers;
• Totally dry working fluid, which means no turbine blade erosion, giving the system high reliability and reduced maintenance costs as well as fewer controls;
• Lower operational pressures (20 bar max), which mean safer operation, less bureaucratic prodlems and reduced plant costs;
• No atmospheric emissions (closed circuit operation);

From an environmental standpoint, ZE systems are reproachless:

• They recover otherwise wasted resources such as waste heat and byproducts or help tapping renewable sources such as solar and geothermal heat;
• They use plain tap water for thermal energy transfer instead of environmentallydangerous diathermal oil;
• Their working fluid is ozone-friendly, non-toxic, non flammable in liquid form, and 100% biodegradable;
• They are made of recyclable, environmental friendly materials, use a minimum of plastic parts and employ no toxic substances in their construction.

The ZE turbogenerators have been custom designed from scratch for the purpose of being installed in small plants (

• Direct turbine-to-alternator coupling, to eliminate the attrition losses inherent in gearboxes;
• Use of ceramic bearings to prolong operational life and allow very high-rpm operation;
• Custom-designed and sized turbines and power converters for every plant size to obtain optimal mechanical-to electric energy conversion and performance in energy grid output.

Our innovative technology has already been widely field-tested with success in dozens of plants throughout Europe, Asia, Africa and America, from biomass and biogas fueled plants in Italy to solar-assisted plants in Africa, from large farms in the USA to Korean power stations..

All systems by Zuccato Energia are equipped with telecontrol and telediagnostic systems that allow constant monitoring and real-time intervention in case of malfunction through the 3G / GPRS / EDGE cellphone network and any Web-savvy device (PC or tablet).

Besides the aforementioned working fluid, the power generation module is made of various elements, shown in the following diagram.

• Pre-Heater: in this heat exchanger, the heat from the heat source, conveyed to the ORC module by the vector fluid, preheats the working fluid;
• Evaporator: in this heat exchanger, the heat of the vector fluid feeding the ORC module vaporizes the working fluid changing its state from liquid to gas, so increasing its pressure;
• Turbine: propelled by working fluid expansion, it has an ultralight impeller that reaches very high rotational speed (12-18.000 rpm) drawing along the generator rotor assembly;
• Synchronous Electric Generator: spinning at high speed thanks to its direct connection with the turbine, it produces electric power.
• Inverter: Ensures generator output meets all specifications (phase, frequency and voltage) to interface with the national power grid;
• Regenerator: pre-preheats the incoming working fluid using the heat from the working fluid itself downstream of the turbine, to increase system efficiency;
• Condenser: reduces the temperature of the working fluid gas downstream of the turbine, to make it go back to its originary liquid state;
• Storage tank to keep the condensed working fluid in liquid form;
• Recirculation pump to pump the fluid back in the ORC loop.

These are the estimated process data for the plant:

Preheater +Evaporator

• Total thermal power input: 740 kWr
• Vector fluid: Overheated water
• Vector fluid temperature (input / output): 2l60°C /145°C
• Vector fluid flow rate: 11,91 kg/s

Condenser

• Thermal power dissipation: 471 kWT
• Condenser cooling water temperature (in/out): 32°C /40°C
• Condenser circuit flow: 14.07 kg/s

Vector fluid is the fluid that is used to convey heat from the heat source to the ORC module where its heat is used to evaporate the working fluid described in the next page.

The two fluids operate in separate loops and never mix - only heat is transferred between them.

Zuccato Energia has chosen to use plain tap water as a vector fluid instead of diathermal oil which, while maybe slightly more efficient at heat transfer, is far more dangerous to use, as it is flammable and potentially polluting if spilled.

In this plant, the vector fluid is overheated water at 160°C - i.e. water heated above the boiling point but kept liquid under pressure.

The high-performance organic working fluid is the key component that allowed Zuccato Energia to create its ORC plants, granting optimal performances due to its excellent specifications:

• Wide operating temperature range that allows tapping into low-quality heat sources that were previously considered as unexploitable;
• High condensing temperature allowing the use of standard cooling towers;
• Totally dryiness when in gas form , so no cavitation and no turbine blade erosion;
• Low operational pressures granting better safety, less bureaucratic problems, lower costs;
• Totally ozone-friendly, non toxic, 100% biodegradable and non-flammable in liquid form, so it is environment-friendly and any accidental leaks are neither harmful or dangerous;
• Closed-loop operation means almost no need for refills, no steam nor water consumption and no emissions, so plants can be cheaper to operate, simpler and more compact than equivalent steam-based ones.

The fluid inside the plant undergoes several phase changes and treatments; the process specifications are resumed in the following table:

Working Fluid

• Type: Mixture of environment-friendly, non-toxic, non-flammable HFCs
• Operational range: 60-16 5°C
• Condensation temperature: ~33°C
• Working pressure: max. 20 bar
• Input temperature: 145 °C
• Input pressure: 16,08 bar
• Condenser output pressure: 1,17 bar
• Organic vapor mass flow: ~5,26kg/s(145/40°C)

The following tables show the main technical specification of the ORC power generation module turbine and its attached generator and inverter.

Turbine

• Type: Single-stage radial inflow turbine w/fixed nozzles, directly coupled to the generator shaft
• Operating Temperature (input/Output): 145°C/-100°C
• Stage pressure: PS 16 (tested to 24 bar)
• Materials: Machined steel [body) / Aluminium alloy ompeiieo
• Speed control: Feedback loop on the generator current output
• Seals and gaskets: Sealed labyrinth on impeller back and optionally at generator interface. Environmental seal using gaskets and O-rings

Generator

• Type: Synchronous, permanent magnet
• Power Output: 100kWe
• Rotational Speed: 15.000 Rpm(12...18 kRpm)
• Rectifier/synchronizer: Built-in/Included
• Output voltage: 503-577 VAC @ 500Hz
• Cooling system: Water jacket, 15 KWt heat dissipation
• Cooling fluid: Water + glycol mix @ Tih
• Additional cooling (optional): Working fluid injection
• Pressure seal: 2,5 bar (gas seal)

Inverter

• Type: IGBT- mains synchronized
• Output power: 100 kWe
• Output voltage: 400V+5%Tol.
• Output frequency: 50Hz+0,5%Tol.
• Cooling: Air-cooled
• Max operational environmental temperature: 40°C
• Braking chopper: Built-in, 100 kW

Heat Exchangers

The heat exchangers used in this power generation module are of the brazed plate type - the most compact and efficient solution for several applications. Made by brazing several quality corrugated steel plates together, taking care first to turn the fishbone-shaped corrugations on each plate 180° from the next one, these exchangers have very small fluid-passing sections, so their heat exchange-to-encumbrance ratio great. Their most important characteristics are:

• Small size : they occupy down to 10% of the space other exchanger types require, making transport easier and the plant smaller.
• Low temperature differentials: they can work with minimal temperature differences between cooling fluid and cooled fluid, thus increasing overall system efficiency;
• Low load losses: in most cases, even lower than those of a coaxial exchanger.
• Resistance to dirt and corrosion: high fluid turbulence and total use of the available surface means a drastic reduction in deposits due to material contained in the fluids. What’s more, they may be perfectly cleaned using normal detergent fluids. Corrosion problems are avoided by using specifically resistant materials in their construction.

Heat Exchangers

• Type: Brazed plate
• Working pressures: 30 bar (Nominal)/ 39 bar (Test)/225 bar (Burst)
• Construction materials: AISI316 S/Steel& 99,9% copper
• Max working temperature: 195°C

Condensation Tank

Required to keep an adequate reserve of liquid working fluid for the plant, it is made of rustproofed carbon steel with PN25 connections, has a capacity of 180 litres and is equipped with a built-in level sensor.

Working Fluid Pump

Required to make the condensed working fluid flow back into the ORC loop, its motor is of the closed short-circuited cage type with external ventilation . Energy-efficient (class I), it has IP55 protection and is certified to the EN 60034-1 standard. Equipped with class F insulation (Tmax=155°C), its hydraulic part is kept in place between the upper cap and the pump body by tie rods.

Control Panel

The control panel hosts all control, supervision, automation and communication electronics for the power generation module. It contains :

• Process management electronics;
• Temperature and pressure control electronics;
• Alarm management systems;
• Mains connection systems and inverter circuitry for power factor correction;
• Mains interface panel with low-voltage protection circuitry.

 The control panel also include a built-in cellular modem router that allows password-protected, policy-regulated remote access and system control through the Internet.

The power generation module is supplied mounted on a self-supporting compact frame (“skid”) which houses all the principal components, except for the optional cooling tower, which is a separate system (see next page).

The following drawings show the standard version of the ZE-75-LT ORC power generation module, which weighs about 5 tons an is designed for indoor installation.

A closed, weatherproof version of the skid for outdoor installation is also available.

Please keep in mind that the skid requires at least 1.5 meters of free space on all sides for easy maintenance access.

Zuccato Energia, being the system developer and manufacturer may also build the skid in nonstandard dimensions different from the above, to tailor the system on the client’s needs.