I have low temperature waste heat; can I use a heat pump to increase the temperature of that heat and use a turbine to generate power?
Short answer: No.
While this might seem like a good idea at first glance, after some thinking, you will realise that it really isn’t. Due to the second law of thermodynamics, you will never be able to generate more power in the turbine than the heat pump is consuming. Due to inefficiencies and losses, you will use considerably more power to the heat pump than the turbine can generate.
It does not matter what kind of heat pump or power generation unit you are using. If it was possible, you could make a machine that can do work indefinitely without an external energy source, i.e. a perpetuum mobile.
Do I need both a heat sink and a heat source to use a heat pump? The hot stream is cold when it enters the heat pump.
Yes, the heat pump needs both something to heat up as well as something to cool down. If you look at the energy balance you will notice that taking away the (cold) heat source turns the heat pump into an electric heater.
Why is the Coefficient of Performance (COP) so low? At home my heat pump has much higher COP
The COP varies with the temperatures. With a higher difference in the sink and source temperatures, the COP will go down. For high temperature heat pumps the difference is often high, which means a lower COP is possible than for low temperature heat pumps. For example:
If you want to make ice water at 0°C and use the heat to generate 1 barg steam (120°C), the theoretical maximum COPh is 3.3. For a HighLift heat pump, the COPh would be around 1.8, or around 54% of the theoretical maximum. Note that in this case you will also get cooling, so the COPtotal would be around 2.5.